Prognostic value of tumor-infiltrating lymphocytes in patients with triple-negative breast cancer: a systematic review and meta-analysis

DOI: https://doi.org/10.21203/rs.2.19214/v1

Abstract

Objective

The objective of this systematic review and meta-analysis is to determine prognostic roles of the total tumor-infiltrating lymphocytes (TILs) or subtypes of TILs (CD4+, CD8+, and FOSP3+) for patients with triple-negative breast cancer (TNBC).

Methods

A systematic literature search was conducted in the databases of MEDLINE, EMBASE, and Web of Science to identified eligible articles before August 2019. Study screening, data extraction, and risk of bias were performed by two independent reviewers. Risk of bias on study level was assessed using an approach based on the ROBINS I tool and the Quality In Prognosis Studies (QUIPS) tool. We performed meta-analyses to obtain a pooled estimate of the prognostic role of TILS using Review Manager 5.3.

Results

There was total of 37 studies included in the final analysis. Compared to TNBC patients with poor TILs, TNBC patients with rich TILs had a higher pCR to treatments (OR 2.14, 95% CI 1.43-3.19). Along with per 10% increase of the TILs, patients with TNBC had an increased pCR (OR 1.09, 95% CI 1.02-1.16). Compared to TNBC patients with poor TILs, patients with rich TILs had a better OS (HR 0.58, 95% CI 0.48-0.71) and DFS (HR 0.66, 95% CI 0.57-0.76). Addition to, along with a continuous increase of the TILs, patients with TNBC had improved OS (HR 0.90, 95% CI 0.87-0.93) and DFS (HR 0.92, 95% CI 0.90-0.95) as well. CD4+TILs subgroup (rich vs. poor) showed a better OS (HR 0.49, 95%CI 0.32-0.76) and DFS (HR 0.54, 95%CI 0.36-0.80). CD8+TILs subgroup (rich vs. poor) showed a better DFS (HR 0.55, 95% CI 0.38-0.81), but no statistical association was found with OS (HR 0.70, 95% CI 0.46-1.06). FOXP3+TILs subgroup (rich vs. poor) showed a better DFS (HR 0.50, 95% CI 0.33-0.75), but no statistical association was found with OS (HR 1.28, 95% CI 0.24-6.88).

Conclusion

TNBC with higher levels of TILs showed better short-term and long-term prognosis. The phenotypes of TILs (CD4+TILs, CD8+TILs, and FOXP3+TILs) had positive prediction for long-term prognosis for TNBC.

Background

Triple-negative breast cancer (TNBC) is the term used to describe breast cancer cases that lack expression of estrogen receptor (ER), human epidermal growth factor receptor-2 (HER2), and progesterone receptor (PR) [1]. TNBC is characterized by a poor prognosis, and accordingly, the 5-year survival rate is only around 60% [2]. As the malignancy of breast cancer depends not only on its genetic abnormalities and biological characteristics but also on interactions between the cancer cells and their microenvironment, it is vital to understand the tumor microenvironment [3].

The microenvironment of breast cancer contains a variety of cell types, including tumor-infiltrating lymphocytes (TILs). Accumulating evidence indicates that TILs play essential roles in carcinogenesis and cancer progression [4]. Furthermore, interleukin (IL)-6 and IL-8 secreted by some subtypes of lymphocytes can generate a positive feedback loop between the immune microenvironment and tumor cells [5]. According to the results of a meta-analysis in 2014, the level of TILs was positively associated with a the prognosis of TNBC [6]. However, various subtypes of TILs have both inhibitory and stimulatory effects on the prognosis and progression of breast cancer. The (cluster of differentiation) CD4+ T cells and CD8+ T cells (primary effector TIL subtypes) have been linked to a better response to systemic treatment in breast cancer [7, 8]. On the contrary, forkhead box P3 (FOXP3)+ T-cell infiltration was found to predict a worse prognosis via the mediation of tumor immune escape [9, 10]. Because TNBC has unique clinicopathological and immunohistochemical features, determining the clinical associations of the total TIL count or the levels of specific subtypes of TILs in TNBC can improve our ability to predict the prognostic pattern and treatment response for TNBC.

The objective of the present systematic review and meta-analysis was to determine the prognostic roles of the total TILs or the levels of subtypes of TILs (CD4+, CD8+, and FOXP3+) in TNBC.

Methods

The present systematic review and meta-analysis were conducted following the requirements of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement [11].

Search strategy and study selection

A systematic literature search was conducted using the MEDLINE, EMBASE, and Web of Science databases to identify eligible articles published before August 2019. The keywords used for the literature search included triple-negative breast cancer (TNBC), TILs, prognosis, and survival. Review and meta-analysis articles were scanned for additional relevant studies. The literature search strategies are outlined in Appendix I.

Outcome definitions

Pathological complete response (pCR) was defined as the absence of all invasive disease cells and lymph node metastasis [12]. Overall survival (OS) was defined as the period from the date of TNBC diagnosis to the time of death with any cause [13]. Disease-free survival (DFS) was defined as the period from the start of treatment to the first recurrence, or to death without any type of relapse [13].

Inclusion and exclusion criteria

The inclusion criteria were the following: (1) paper written in English, (2) study population or study sub-group consisted of patients with TNBC, (3) the relationships between TIL levels and short-term prognosis (i.e., pCR) and long-term prognosis (i.e., OS and DFS) were investigated, (4) original studies without restriction in study design, (5) studies containing enough data to estimate the effects (i.e., hazard ratios [HRs] and corresponding 95% confidence intervals [CIs] for OS or DFS, and odds ratios [ORs] and corresponding 95% CIs for pCR). The exclusion criteria were the following: (1) reviews, commentaries, editorials, protocols, case reports, qualitative research, or letters; (2) duplicate publications; and (3) full text not published in English, and (4) studies without usable data.

Study selection and quality assessment

Title–abstract screening was performed first to determine eligibility by two independent reviewers. Full-text articles that passed the first stage screening were downloaded for further review according to the inclusion and exclusion criteria. Disagreements were resolved by consultation with a third author or by joint discussion.

As no randomized controlled trial was found, we assessed the risk of bias using an approach based on the ROBINS I (“Risk Of Bias In Non-randomised Studies - of Interventions”) tool [14] and the Quality In Prognosis Studies (QUIPS) tool [15]. The risk of bias assessment was conducted by two reviewers independently.

Data extraction

We extracted data from the included studies using a pilot-tested data extraction form. We extracted the following data for this review: (1) first author and publication year, (2) country in which study was conducted, (3) study design, (4) participant details, (5) duration of follow-up, (6) choice of cut-off scores for defining positive TILs, (7) TIL category, (8) TIL measurement details (category or continuous), (9) adjusted HRs with 95% CIs for OS and/or DFS (univariable HRs were recorded only if adjusted HRs were not available), and (10) adjusted ORs with 95% CIs (or accurate event numbers) for pCR (univariable ORs were recorded only if adjusted ORs were not available).

Statistical analysis

We performed meta-analyses to obtain a pooled estimate of the prognostic role of TILs using RevMan 5.3. Category software, and continuous TILs were estimated separately to decrease the heterogeneity. The results were expressed as HR (95%CI) for OS and DFS and by OR (95% CI) as calculated by Review Manager 5.3 [16]. A P-value less than 0.05 was set as indicative of statistical significance. Between-study heterogeneity was measured using the Higgins I2 statistic and Cochrane’s Q test (P < 0.10 or I2 > 50% was considered indicative of statistically significant heterogeneity) [17]. A random effect model (Der Simonian and Laird method) was applied if heterogeneity was present. However, the fixed-effect model was used in the absence of between-study heterogeneity (P > 0.10 or I2 < 50%). We performed subgroup analyses according to different subtypes of TILs as a sensitivity analysis to confirm the robustness of our results. Funnel plots were drafted for each meta-analysis to assess the potential publication bias.

Results

Search results and study characteristics

A total of 3194 articles were selected through searching the chosen electronic databases, and an additional 5 records were identified by cross-checking the bibliographies of retrieved meta-analysis or relevant reviews. After exclusion of duplicates, we screened the titles and abstracts and identified 46 articles for full-text review. We eliminated 9 papers according to the inclusion/exclusion criteria. Ultimately, 37 papers were included in the final analysis (Fig. 1) [7, 1853].

The basic characteristics and target outcomes extracted from the included studies are listed in Table 1. All included articles (n = 37) were full-reported retrospective cohort studies. The studies were conducted in the United States (18.9%, 7/37), Japan (16.2%, 6/37), South Korea (16.2%, 6/37), China (8.1%, 3/37), France (8.1%, 3/37), Italy (3.4%, 2/37), Singapore (3.4%, 2/37), Germany (5.4%, 2/37), Australia (2.7%, 1/37), Peru (2.7%, 1/37), Spain (2.7%, 1/37), Canada (2.7%, 1/37), Ireland (2.7%, 1/37), and Switzerland (2.7%, 1/37). The population targeted was patients with TNBC. Eleven studies (29.7%, 11/37) provided evidence of the prognostic value of TILs for short-term outcomes (pCR), and five (75.7%, 28/37) provided evidence of the prognostic values of TILs for long-term outcomes (OS and/or DFS). The details of data extraction are presented in Appendix II.

Table 1
Clinical details of the included studies.
Author, year of publication
Country
Type of TNBC
No. of participants
TIL detection method
Location of TILs
Definition of high TIL level
TIL phenotype
Median follow-up (m)
Short-term prognosis
Target long-term prognosis
Adams et al. 2014[18]
USA
Operable TNBC
481
HE
Intra-epithelial and stromal
TILs involving 50% of either tumor stroma or cell nests
None specified
127
not specified
DFS
OS
AiErken et al. 2017[19]
China
TNBC
215
HIC
Total and stromal
TILs-low (range, 0–10%); TILs-moderate (range, 11–40%); TILs-Marked (range, 41–100%).
PD-L1
67.7
not specified
DFS
OS
Althobiti et al. 2018[20]
USA
TNBC
230
HE
Average stromal
Quantity of TILs was evaluated as percentage of TILs present in the stroma
CD3+
CD8+
FOXP3+
CD20+
CD68+
not specified
not specified
OS
Asano et al. 2018[21]
Japan
TNBC
61
HE
Stromal
> 10% was considered positive for TILs
None specified
40.8
pCR
DFS
Byun et al.
2018[22]
South Korea
TNBC
109
IHC
not specified
TILs were divided into (≥ 33% vs. <33%)
PD-L1 expression was categorized into two groups according to the final scores: low expression (< 100) and high expression (≥ 100).
PD-L1+
TILs
76
not specified
DFS
OS
Cerbelli et al. 2017[23]
Italy
TNBC received standard NACT (4 cycles of doxorubicin + cyclophosphamide Q3W followed by 12 cycles of paclitaxel weekly)
54
IHC and HE
Stromal
TILs were quantified as a percentage of the stromal area of the tumor and expressed as a continuous parameter.
PD-L1
not specified
pCR
not specified
Denkert et al. 2015[24]
Germany
TNBC
255
IHC and HE
Stromal
TILs involving 60% of either tumor stroma or cell nests
PD1
PDL1
CD8+
FOXP3
not specified
pCR
not specified
Denkert et al. 2018[25]
Germany
TNBC
906
HE
Stromal
Three predefined categories: low TILs (0–10%), intermediate TILs (11–59%), or high TILs (60–100%).
None specified
for
OS, 62.8 months; median follow-up for DFS, 63.3 months
pCR
DFS
OS
Dieci et al. 2014[26]
France
TNBC patients with residual disease
293
HE
Intratumoral and stromal
High-TIL if It-TIL and/or Str-TIL > 60%
None specified
75.6
not specified
OS
Dieci et al. 2015[27]
France
TNBC
199
HE
Intratumoral and stromal
Cases were defined as High-TIL if It-TIL and/or Str-TIL > 60%
None specified
152.4
not specified
OS
Galvez et al. 2018[28]
Peru
TNBC
100
HE
Stromal
Cases were defined as High-TIL if Str-TIL > 50%
None specified
not specified
pCR
not specified
Goto et al. 2018[29]
Japan
TNBC treated with neoadjuvant chemotherapy
39
HE and IHC
Stromal
High if TILs occupied > 10% of the stromal area
CD8+
FOXP3+
not specified
not specified
OS
Herrero-Vicent et al. 2017[30]
Spain
TNBC treated with neoadjuvant chemotherapy
164
HE
None specified
not specified
not specified
not specified
pCR
not specified
Hida et al. 2016[31]
Japan
TNBC
381
HE
None specified
Classified as high if TILs score > 50%
not specified
45
pCR
not specified
Jang et al. 2018[32]
South Korea
TNBC
231
HE
Stromal
Classified TILS as high (> 10%)
not specified
117
not specified
DFS
OS
Kim et al. 2017[33]
South Korea
TNBC
40
HE
Stromal
Classified TILS score as high (> 60%).
Glutaminase+TILs
78.3
not specified
DFS
Krishnamurti et al. 2017[34]
USA
TNBC without neoadjuvant treatments
157
HE
Stromal
TILs estimated in intervals as < 5%, 5–10%, 11–50%, and > 50%
not specified
not specified
not specified
DFS
OS
Lee et al. 2016[35]
South Korea
TNBC
769
HE
Stromal
TILs defined as the mean percentage of stroma of invasive carcinoma infiltrated by lymphocytes and plasma cells in 10% increments
not specified
not specified
not specified
DFS
OS
Leon-Ferre et al. 2018[36]
USA
TNBC
605
HE
Stromal and intratumoral
Lymphocyte-predominant breast cancer (LPBC) was defined as having > 50% stromal or intratumoral TILs
not specified
124.8
not specified
DFS
OS
Li et al. 2016[37]
USA
TNBC
136
IHC and HE
not specified
TILs were evaluated as the percentage of intratumoral stroma covered by mononuclear lymphocytes.
PD-L1
PD-1
49.03
not specified
DFS
OS
Loi et al. 2014[38]
Australia
newly diagnosed TNBC
145
HE
Stromal
TILs ≥ 50%
not specified
62
not specified
OS
Luen et al. 2019[39]
France
TNBC treated with neoadjuvant chemotherapy
375
HE and IHC
Stromal
Quantification of TILs in the tumor stroma was recorded as a percentage of occupied stromal areas.
not specified
72
not specified
OS
Matsumoto et al. 2016[40]
Singapore
Primary TNBC
232
HE and IHC
Stromal and intratumoral
Median TIL value as the cut-off for high vs. low
CD4+
CD8+
not specified
not specified
DFS
OS
McIntire et al. 2018[41]
USA
TNBC
76
HE and IHC
None specified
TILs within the entire tumor were estimated at 5% intervals
CD8+
110
not specified
DFS
OS
Miyashita et al. 2014[42]
Japan
TNBC
110
IHC
Stromal and intratumoral
None specified
CD8+
FOXP3+
not specified
pCR
not specified
Mori et al. 2017[43]
Japan
TNBC
248
IHC
Stromal and intratumoral
PD-L1+
was defined as expression in ≥ 5% of TILs
PD-L1
68
not specified
OS
O'Loughlin et al. 2018[44]
Ireland
TNBC
75
HE
stromal
LPBC was defined as having > 50% stromal TILs
None specified
not specified
pCR
not specified
Ono et al. 2012[45]
Japan
TNBC received NAC and subsequent surgical therapy
102
IHC
None specified
TIL score classified as high if the sum was 3–5
None specified
not specified
pCR
not specified
Park et al. 2016[46]
South Korea
Early TNBC
133
HE
Stromal and intratumoral
Classified TILS as high (> 10%)
not specified
None specified
not specified
DFS
OS
Pruneri et al. 2016[47]
USA
TNBC
724
Multiplexed QIF staining
Stromal
LPBC defined as > 50% stromal TILs
not specified
82.8
not specified
DFS
OS
Pruneri et al. 2016[48]
Switzerland
TNBC
897
HE
Stromal
None specified
not specified
98.4
not specified
DFS
OS
Ruan et al. 2018[49]
China
TNBC treated with neoadjuvant chemotherapy
166
None specified
Stromal and intratumoral
Classified TILS as high (> 10%)
not specified
not specified
pCR
not specified
Seo et al. 2013[7]
South Korea
TNBC
38
IHC
None specified
Median values of TILs used as cut off, and infiltration of TILs categorized as low or high.
CD4+
CD8+
FOXP3+
not specified
pCR
not specified
Tian et al. 2016[50]
China
Primary invasive TNBCs
425
HE
Stromal and intratumoral
LPBC was categorized as tumors involving ≥ 50% lymphocytic infiltration in either tumor stroma or cell nests
not specified
48
not specified
DFS
OS
Urru et al. 2018[51]
Italy
TNBC
841
IHC
Stromal
None specified
not specified
51.6
not specified
DFS
OS
West et al. 2013[52]
Canada
TNBC
82
IHC
Stromal
None specified
FOXP3+TILs
not specified
not specified
DFS
Yeong et al. 2017[53]
Singapore
TNBC
164
IHC
None specified
Cut-off median percentages used were also compatible to the accepted clinical pathological practices
FOXP3+
not specified
not specified
DFS
OS
Abbreviations: TNBC, triple negative breast cancer; HE, hematoxylin-eosin; TNP, triple-negative phenotype; AC, doxorubicin plus cyclophosphamide; AT, doxorubicin plus paclitaxel; DFS, disease-free survival; OS, overall survival; IHC, immunohistochemistry; pCR, pathological complete response; LPBC, lymphocyte-predominant breast cancer; CMF, cyclophosphamide methotrexate fluorouracil; ACT, doxorubicin plus cyclophosphamide followed by docetaxel; AD, doxorubicin plus docetaxel.

TILs and pCR

From the 11 studies demonstrating the prognostic value of TILs for pCR among TNBC patients, the results showed that upregulation of TILs predicted a higher pCR rate. The pooled ORs were 2.14 (95% CI, 1.43–3.19) for TIL level (high vs. low) and 1.09 (95% CI, 1.02–1.16) for continuous TILs (10% increase in TIL level). When stratified by the TIL phenotypes of CD4+, CD8+, and FOXP3+, no statistical differences in pCR were found in the subgroup analysis. The details pooled results are presented in Fig. 2.

TILs and OS

A total of 24 studies supported the prognostic value of TILs for OS in TNBC patients. The results showed upregulation of TILs predicted a better OS. The pooled HRs were 0.58 (95% CI, 0.48–0.71) for total TIL level (high vs. low) and 0.90 (95% CI, 0.87–0.93) for continuous TILs (Fig. 3).

From subgroup analyses according to TIL phenotype (high vs. low), the HRs were 0.49 (95% CI, 0.32–0.76), 0.70 (95% CI, 0.46–1.06), and 1.28 (95% CI, 0.24–6.88) for CD4+ TILs, CD8+ TILs, and FOXP3+ TILs, respectively (Fig. 3A). Subgroup analyses according to the change in TIL level (continuous) returned HRs of 0.50 (95% CI, 0.28–0.89) and 1.80 (95% CI, 0.50–6.48) for CD8+ TILs and FOXP3+ TILs, respectively (Fig. 3B).

TILs and DFS

A total of 20 studies supported the prognostic value of TILs for DFS in TNBC patients. The results showed upregulation of TILs predicted better DFS, with pooled HRs of 0.66 (95% CI, 0.57–0.76) for TIL level (high vs. low) and 0.92 (95% CI, 0.90–0.95) for continuous TILs (Fig. 4).

From subgroup analyses according to TIL phenotype (high vs. low), the HRs were 0.54 (95% CI, 0.36–0.80), 0.55 (95% CI, 0.38–0.81), and 0.50 (95% CI, 0.33–0.75) for CD4+ TILs, CD8+ TILs, and FOXP3+ TILs, respectively (Fig. 4A).

Subgroup analyses according to the change in TIL level (continuous) returned HRs of 0.93 (95% CI, 0.90–0.96), 0.70 (95% CI, 0.39–1.27), and 0.41 (95% CI, 0.21–0.80) for a 10% increase in TILs, continuous TILs, and a 5% increase in TILs of each subgroup, respectively (Fig. 4B).

Risk of bias in included studies

We evaluated the risk of bias for all included studies (n = 37). We found the main sources of bias were related to missing data, TIL measurement and confounding controls. Figure 5A shows the risk of bias assessments for each cohort. Evaluations for each domain across full reported studies are shown in Fig. 5B.

Publication bias

Funnel plot analysis did not indicate apparent publication bias affecting the HRs for DFS and OS or the ORs for pCR in the included studies (Fig. 6).

Discussion

As TNBC is a poor prognostic subtype of breast cancer, it is important to identify biomarkers that can rigorously predict its prognosis. The present review and meta-analysis synthesized 37 studies to evaluate the association between TIL levels, both total and specific subtypes, and prognosis in TNBC patients. Our findings indicate that a high TIL level in TNBC significantly increases the likelihood of pCR and improves DFS and OS.

In the present study, we used pCR as the indicator of short-term prognosis for patients with TNBC. Previous studies reported that higher TIL levels predict a better response to chemotherapy in patients with breast cancer [5456]. According to our pooled results, compared to TNBC patients with low TIL levels, TNBC patients with high TIL levels had a higher rate of pCR to treatment (OR 2.14, 95% CI 1.43–3.19). Moreover, with each 10% increase in TIL level, patients with TNBC had an increased pCR rate (OR 1.09, 95% CI 1.02–1.16). A potential explanation for these findings is the influence of TILs to tumor immunosurveillance and tumor immunosuppression [57]. However, no significant pCR improvement was observed for high levels of the CD4+, CD8+, and FOXP3+ TIL subgroups. This may due to the limited amount of data available for these subgroups.

The indicators of long-term prognosis in this study were OS and DFS. According to our pooled results, compared to TNBC patients with low TIL levels, patients with high TIL levels showed better OS (HR 0.58, 95% CI 0.48–0.71) and DFS (HR 0.66, 95% CI 0.57–0.76). Additionally, with a continuously increasing TIL levels, patients with TNBC had improved OS (HR 0.90, 95% CI 0.87–0.93) and DFS (HR 0.92, 95% CI 0.90–0.95). This finding is consistent with previous conclusions [3, 9, 25, 58, 59]. Our results indicate that a high level of TILs is a positive predictor for the prognosis of patients with TNBC.

The CD4+ TIL subgroup (high vs. low) showed a better OS (HR 0.49, 95%CI 0.32–0.76) and DFS (HR 0.54, 95%CI 0.36–0.80), and the CD8+ TIL subgroup (high vs. low) showed a better DFS only (HR 0.55, 95% CI 0.38–0.81). Nevertheless, the pooled results indicated CD4+ TILs and CD8+ TILs were positive predictors for long-term prognosis in TNBC. This is consistent with previous meta-analysis results [6]. The FOXP3+ TIL subgroup (high vs. low) also showed only better DFS (HR 0.50, 95% CI 0.33–0.75), with no statistical association with OS (HR 1.28, 95% CI 0.24–6.88). This finding for FOXP3+ TILs is opposite to that of previous meta-analyses [3, 6], and the reason for this inconsistency is unclear. More studies of the association of FOXP3+ TILs with the prognosis of TNBC are needed.

To our best knowledge, this was the first meta-analysis to pool the prognostic results for categorical TIL level and continuous TILs separately. Therefore, from the results, we can definitively conclude that a higher density of TILs corresponds to a better prognosis for TNBC. Our study does have some limitations. First, all included studies were retrospective cohort studies, with risks of bias related to missing data, TIL measurement, and confounding controls. Another limitation was variation in the definition of high TIL level among the included studies.

Conclusions

TNBC with higher levels of TILs showed better short-term and long-term prognoses. High levels of specific phenotypes of TILs (CD4+, CD8+, and FOXP3+) could positively predict the long-term prognosis for TNBC.

Abbreviations

TILs

tumor-infiltrating lymphocytes

TNBC

triple-negative breast cancer

ER

estrogen receptor

HER2

human epidermal growth factor receptor 2

PR

progesterone receptor

PRISMA

Systematic Reviews and Meta-Analyses

IL

interleukin

CD

cluster of differentiation

FBP3

forkhead box P3

pCR

Pathological complete response

OS

Overall survival

DFS

Disease-free survival

HR

hazard ratios

CI

confidence intervals

OR

odds ratio

ROBIN I

Risk Of Bias In Non-randomised Studies - of Interventions

QUIPS

Quality In Prognosis Studies

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

All authors have read and approved the content and agree to submit it for publication. Consent to publish from the patient is not applicable.

Competing interests

Authors declare there is no competing interest.

Funding

This study was supported by the National Key Technologies R&D Program (No. 2015BAI13B09) and the Research Foundation of Beijing Friendship Hospital, Capital Medical University (No. YYQDKT2018-11). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Authors’ contributions

GG carried out the initial background research and drafted the manuscript. GG and ZW acted as independent reviewers in screening literature, extracting data, and assessing the quality of each study. GG, ZZ and XQ helped in developing the manuscript or revising it critically for important intellectual content. All authors gave final approval of the version to be published.

Acknowledgments

The authors would like to thank all of the involved study investigators for dedicating their time and skills to the completion of this study.

References

  1. Foulkes WD, Smith IE, Reis-Filho JS: Triple-Negative Breast Cancer. New England Journal of Medicine 2010, 363(20):1938-1948.
  2. Isakoff SJ: Triple-negative breast cancer: role of specific chemotherapy agents. Cancer journal (Sudbury, Mass) 2010, 16(1):53-61.
  3. Yu X, Zhang Z, Wang Z, Wu P, Qiu F, Huang J: Prognostic and predictive value of tumor-infiltrating lymphocytes in breast cancer: a systematic review and meta-analysis. Clinical & translational oncology : official publication of the Federation of Spanish Oncology Societies and of the National Cancer Institute of Mexico 2016, 18(5):497-506.
  4. Perdiguero EG, Geissmann F: Identifying the infiltrators. Science 2014, 344(6186):801-802.
  5. Korkaya H, Liu S, Wicha MS: Breast cancer stem cells, cytokine networks, and the tumor microenvironment. The Journal of clinical investigation 2011, 121(10):3804-3809.
  6. Ibrahim EM, Al-Foheidi ME, Al-Mansour MM, Kazkaz GA: The prognostic value of tumor-infiltrating lymphocytes in triple-negative breast cancer: a meta-analysis. Breast cancer research and treatment 2014, 148(3):467-476.
  7. Seo A, Lee H, Kim E, Kim H, Jang M, Lee H, Kim YJ, Kim JH, Park SY: Tumour-infiltrating CD8+ lymphocytes as an independent predictive factor for pathological complete response to primary systemic therapy in breast cancer. British journal of cancer 2013, 109(10):2705.
  8. Liu S, Lachapelle J, Leung S, Gao D, Foulkes WD, Nielsen TO: CD8+ lymphocyte infiltration is an independent favorable prognostic indicator in basal-like breast cancer. Breast cancer research : BCR 2012, 14(2):R48.
  9. Stanton SE, Disis ML: Clinical significance of tumor-infiltrating lymphocytes in breast cancer. Journal for immunotherapy of cancer 2016, 4:59.
  10. Takenaka M, Seki N, Toh U, Hattori S, Kawahara A, Yamaguchi T, Koura K, Takahashi R, Otsuka H, Takahashi H: FOXP3 expression in tumor cells and tumor-infiltrating lymphocytes is associated with breast cancer prognosis. Molecular and clinical oncology 2013, 1(4):625-632.
  11. Liberati A, Altman DG, Tetzlaff J, Mulrow C, Gotzsche PC, Ioannidis JP, Clarke M, Devereaux PJ, Kleijnen J, Moher D: The PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate health care interventions: explanation and elaboration. Journal of clinical epidemiology 2009, 62(10):e1-34.
  12. Fisher B, Bryant J, Wolmark N, Mamounas E, Brown A, Fisher ER, Wickerham DL, Begovic M, DeCillis A, Robidoux A et al: Effect of preoperative chemotherapy on the outcome of women with operable breast cancer. Journal of clinical oncology : official journal of the American Society of Clinical Oncology 1998, 16(8):2672-2685.
  13. Ovcaricek T, Frkovic S, Matos E, Mozina B, Borstnar S: Triple negative breast cancer-prognostic factors and survival. Radiology and oncology 2011, 45(1):46-52.
  14. Sterne JA, Hernan MA, Reeves BC, Savovic J, Berkman ND, Viswanathan M, Henry D, Altman DG, Ansari MT, Boutron I et al: ROBINS-I: a tool for assessing risk of bias in non-randomised studies of interventions. Bmj 2016, 355:i4919.
  15. Hayden JA, van der Windt DA, Cartwright JL, Cote P, Bombardier C: Assessing bias in studies of prognostic factors. Annals of internal medicine 2013, 158(4):280-286.
  16. Manager R: Version 5.0. In.: The Nordic Cochrane Centre, The Cochrane Collaboration Copenhagen, Denmark; 2008.
  17. DerSimonian R, Laird N: Meta-analysis in clinical trials. Controlled clinical trials 1986, 7(3):177-188.
  18. Adams S, Gray RJ, Demaria S, Goldstein L, Perez EA, Shulman LN, Martino S, Wang M, Jones VE, Saphner TJ et al: Prognostic value of tumor-infiltrating lymphocytes in triple-negative breast cancers from two phase III randomized adjuvant breast cancer trials: ECOG 2197 and ECOG 1199. Journal of clinical oncology : official journal of the American Society of Clinical Oncology 2014, 32(27):2959-2966.
  19. AiErken N, Shi HJ, Zhou Y, Shao N, Zhang J, Shi Y, Yuan ZY, Lin Y: High PD-L1 Expression Is Closely Associated With Tumor-Infiltrating Lymphocytes and Leads to Good Clinical Outcomes in Chinese Triple Negative Breast Cancer Patients. International journal of biological sciences 2017, 13(9):1172-1179.
  20. Althobiti M, Aleskandarany MA, Joseph C, Toss M, Mongan N, Diez-Rodriguez M, Nolan CC, Ashankyty I, Ellis IO, Green AR et al: Heterogeneity of tumour-infiltrating lymphocytes in breast cancer and its prognostic significance. Histopathology 2018, 73(6):887-896.
  21. Asano Y, Kashiwagi S, Goto W, Takada K, Takahashi K, Hatano T, Takashima T, Tomita S, Motomura H, Ohsawa M et al: Prediction of Treatment Response to Neoadjuvant Chemotherapy in Breast Cancer by Subtype Using Tumor-infiltrating Lymphocytes. Anticancer research 2018, 38(4):2311-2321.
  22. Byun KD, Hwang HJ, Park KJ, Kim MC, Cho SH, Ju MH, Lee JH, Jeong JS: T-cell immunoglobulin mucin 3 expression on tumor infiltrating lymphocytes as a positive prognosticator in triple-negative breast cancer. Journal of Breast Cancer 2018, 21(4):406-414.
  23. Cerbelli B, Pernazza A, Botticelli A, Fortunato L, Monti M, Sciattella P, Campagna D, Mazzuca F, Mauri M, Naso G et al: PD-L1 Expression in TNBC: A Predictive Biomarker of Response to Neoadjuvant Chemotherapy? Biomed Res Int 2017, 2017 (no pagination)(1750925).
  24. Denkert C, von Minckwitz G, Brase JC, Sinn BV, Gade S, Kronenwett R, Pfitzner BM, Salat C, Loi S, Schmitt WD et al: Tumor-infiltrating lymphocytes and response to neoadjuvant chemotherapy with or without carboplatin in human epidermal growth factor receptor 2-positive and triple-negative primary breast cancers. Journal of clinical oncology : official journal of the American Society of Clinical Oncology 2015, 33(9):983-991.
  25. Denkert C, von Minckwitz G, Darb-Esfahani S, Lederer B, Heppner BI, Weber KE, Budczies J, Huober J, Klauschen F, Furlanetto J et al: Tumour-infiltrating lymphocytes and prognosis in different subtypes of breast cancer: a pooled analysis of 3771 patients treated with neoadjuvant therapy. The Lancet Oncology 2018, 19(1):40-50.
  26. Dieci MV, Criscitiello C, Goubar A, Viale G, Conte P, Guarneri V, Ficarra G, Mathieu MC, Delaloge S, Curigliano G et al: Prognostic value of tumor-infiltrating lymphocytes on residual disease after primary chemotherapy for triple-negative breast cancer: a retrospective multicenter study. Annals of oncology : official journal of the European Society for Medical Oncology 2014, 25(3):611-618.
  27. Dieci MV, Mathieu MC, Guarneri V, Conte P, Delaloge S, Andre F, Goubar A: Prognostic and predictive value of tumor-infiltrating lymphocytes in two phase III randomized adjuvant breast cancer trials. Annals of oncology : official journal of the European Society for Medical Oncology 2015, 26(8):1698-1704.
  28. Galvez M, Castaneda CA, Sanchez J, Castillo M, Rebaza LP, Calderon G, De La Cruz M, Cotrina JM, Abugattas J, Dunstan J et al: Clinicopathological predictors of long-term benefit in breast cancer treated with neoadjuvant chemotherapy. World J Clin Oncol 2018, 9(2):33-41.
  29. Goto W, Kashiwagi S, Asano Y, Takada K, Takahashi K, Hatano T, Takashima T, Tomita S, Motomura H, Ohsawa M et al: Predictive value of improvement in the immune tumour microenvironment in patients with breast cancer treated with neoadjuvant chemotherapy. ESMO Open 2018, 3 (6) (no pagination)(e000305).
  30. Herrero-Vicent C, Guerrero A, Gavila J, Gozalbo F, Hernandez A, Sandiego S, Algarra MA, Calatrava A, Guillem-Porta V, Ruiz-Simon A: Predictive and prognostic impact of tumour-infiltrating lymphocytes in triple-negative breast cancer treated with neoadjuvant chemotherapy. ecancermedicalscience 2017, 11 (no pagination)(759).
  31. Hida AI, Sagara Y, Yotsumoto D, Kanemitsu S, Kawano J, Baba S, Rai Y, Oshiro Y, Aogi K, Sagara Y et al: Prognostic and predictive impacts of tumor-infiltrating lymphocytes differ between Triple-negative and HER2-positive breast cancers treated with standard systemic therapies. Breast cancer research and treatment 2016, 158(1):1-9.
  32. Jang N, Kwon HJ, Park MH, Kang SH, Bae YK: Prognostic Value of Tumor-Infiltrating Lymphocyte Density Assessed Using a Standardized Method Based on Molecular Subtypes and Adjuvant Chemotherapy in Invasive Breast Cancer. Annals of surgical oncology 2018, 25(4):937-946.
  33. Kim JY, Heo SH, Choi SK, Song IH, Park IA, Kim YA, Park HS, Park SY, Bang WS, Gong G et al: Glutaminase expression is a poor prognostic factor in node-positive triple-negative breast cancer patients with a high level of tumor-infiltrating lymphocytes. Virchows Archiv : an international journal of pathology 2017, 470(4):381-389.
  34. Krishnamurti U, Wetherilt CS, Yang J, Peng L, Li X: Tumor-infiltrating lymphocytes are significantly associated with better overall survival and disease-free survival in triple-negative but not estrogen receptor-positive breast cancers. Human pathology 2017, 64:7-12.
  35. Lee HJ, Park IA, Song IH, Shin SJ, Kim JY, Yu JH, Gong G: Tertiary lymphoid structures: prognostic significance and relationship with tumour-infiltrating lymphocytes in triple-negative breast cancer. Journal of clinical pathology 2016, 69(5):422-430.
  36. Leon-Ferre RA, Polley MY, Liu H, Gilbert JA, Cafourek V, Hillman DW, Elkhanany A, Akinhanmi M, Lilyquist J, Thomas A et al: Impact of histopathology, tumor-infiltrating lymphocytes, and adjuvant chemotherapy on prognosis of triple-negative breast cancer. Breast cancer research and treatment 2018, 167(1):89-99.
  37. Li XX, Wetherilt CS, Krishnamurti U, Yang J, Ma YM, Styblo TM, Meisel JL, Peng LM, Siddiqui MT, Cohen C et al: Stromal PD-L1 Expression Is Associated With Better Disease-Free Survival in Triple-Negative Breast Cancer. Am J Clin Pathol 2016, 146(4):496-502.
  38. Loi S, Michiels S, Salgado R, Sirtaine N, Jose V, Fumagalli D, Kellokumpu-Lehtinen PL, Bono P, Kataja V, Desmedt C et al: Tumor infiltrating lymphocytes are prognostic in triple negative breast cancer and predictive for trastuzumab benefit in early breast cancer: results from the FinHER trial. Annals of oncology : official journal of the European Society for Medical Oncology 2014, 25(8):1544-1550.
  39. Luen SJ, Salgado R, Dieci MV, Vingiani A, Curigliano G, Gould RE, Castaneda C, D'Alfonso T, Sanchez J, Cheng E et al: Prognostic implications of residual disease tumor-infiltrating lymphocytes and residual cancer burden in triple-negative breast cancer patients after neoadjuvant chemotherapy. Annals of Oncology 2019, 30(2):236-242.
  40. Matsumoto H, Thike AA, Li HH, Yeong J, Koo SL, Dent RA, Tan PH, Iqbal J: Increased CD4 and CD8-positive T cell infiltrate signifies good prognosis in a subset of triple-negative breast cancer. Breast cancer research and treatment 2016, 156(2):237-247.
  41. McIntire PJ, Irshaid L, Liu YF, Chen ZM, Menken F, Nowak E, Shin SI, Ginter PS: Hot Spot and Whole-Tumor Enumeration of CD8(+) Tumor-Infiltrating Lymphocytes Utilizing Digital Image Analysis Is Prognostic in Triple-Negative Breast Cancer. Clin Breast Cancer 2018, 18(6):451-+.
  42. Miyashita M, Sasano H, Tamaki K, Chan M, Hirakawa H, Suzuki A, Tada H, Watanabe G, Nemoto N, Nakagawa S et al: Tumor-infiltrating CD8+ and FOXP3+ lymphocytes in triple-negative breast cancer: its correlation with pathological complete response to neoadjuvant chemotherapy. Breast cancer research and treatment 2014, 148(3):525-534.
  43. Mori H, Kubo M, Yamaguchi R, Nishimura R, Osako T, Arima N, Okumura Y, Okido M, Yamada M, Kai M et al: The combination of PD-L1 expression and decreased tumor-infiltrating lymphocytes is associated with a poor prognosis in triple-negative breast cancer. Oncotarget 2017, 8(9):15584-15592.
  44. O'Loughlin M, Andreu X, Bianchi S, Chemielik E, Cordoba A, Cserni G, Figueiredo P, Floris G, Foschini MP, Heikkila P et al: Reproducibility and predictive value of scoring stromal tumour infiltrating lymphocytes in triple-negative breast cancer: a multi-institutional study. Breast cancer research and treatment 2018, 171(1):1-9.
  45. Ono M, Tsuda H, Shimizu C, Yamamoto S, Shibata T, Yamamoto H, Hirata T, Yonemori K, Ando M, Tamura K et al: Tumor-infiltrating lymphocytes are correlated with response to neoadjuvant chemotherapy in triple-negative breast cancer. Breast Cancer Research & Treatment 2012, 132(3):793-805.
  46. Park HS, Heo I, Kim JY, Kim S, Nam S, Park S, Kim SI: No effect of tumor-infiltrating lymphocytes (TILs) on prognosis in patients with early triple-negative breast cancer: Validation of recommendations by the International TILs Working Group 2014. Journal of surgical oncology 2016, 114(1):17-21.
  47. Pruneri G, Gray KP, Vingiani A, Viale G, Curigliano G, Criscitiello C, Lang I, Ruhstaller T, Gianni L, Goldhirsch A et al: Tumor-infiltrating lymphocytes (TILs) are a powerful prognostic marker in patients with triple-negative breast cancer enrolled in the IBCSG phase III randomized clinical trial 22-00. Breast cancer research and treatment 2016, 158(2):323-331.
  48. Pruneri G, Vingiani A, Bagnardi V, Rotmensz N, De Rose A, Palazzo A, Colleoni AM, Goldhirsch A, Viale G: Clinical validity of tumor-infiltrating lymphocytes analysis in patients with triple-negative breast cancer. Annals of oncology : official journal of the European Society for Medical Oncology 2016, 27(2):249-256.
  49. Ruan M, Tian T, Rao J, Xu X, Yu B, Yang W, Shui R: Predictive value of tumor-infiltrating lymphocytes to pathological complete response in neoadjuvant treated triple-negative breast cancers. Diagnostic pathology 2018, 13(1):66.
  50. Tian T, Ruan M, Yang W, Shui R: Evaluation of the prognostic value of tumor-infiltrating lymphocytes in triple-negative breast cancers. Oncotarget 2016, 7(28):44395-44405.
  51. Urru SAM, Gallus S, Bosetti C, Moi T, Medda R, Sollai E, Murgia A, Sanges F, Pira G, Manca A et al: Clinical and pathological factors influencing survival in a large cohort of triple-negative breast cancer patients. BMC Cancer 2018, 18:11.
  52. West N, Kost S, Martin S, Milne K, Deleeuw R, Nelson B, Watson P: Tumour-infiltrating FOXP3+ lymphocytes are associated with cytotoxic immune responses and good clinical outcome in oestrogen receptor-negative breast cancer. British journal of cancer 2013, 108(1):155.
  53. Yeong J, Thike AA, Lim JCT, Lee B, Li HH, Wong SC, Hue SSS, Tan PH, Iqbal J: Higher densities of Foxp3(+) regulatory T cells are associated with better prognosis in triple-negative breast cancer. Breast cancer research and treatment 2017, 163(1):21-35.
  54. Demaria S, Volm MD, Shapiro RL, Yee HT, Oratz R, Formenti SC, Muggia F, Symmans WF: Development of tumor-infiltrating lymphocytes in breast cancer after neoadjuvant paclitaxel chemotherapy. Clin Cancer Res 2001, 7(10):3025-3030.
  55. Liu S, Duan X, Xu L, Xin L, Cheng Y, Liu Q, Ye J, Zhang S, Zhang H, Zhu S: Optimal threshold for stromal tumor-infiltrating lymphocytes: its predictive and prognostic value in HER2-positive breast cancer treated with trastuzumab-based neoadjuvant chemotherapy. Breast cancer research and treatment 2015, 154(2):239-249.
  56. West NR, Milne K, Truong PT, Macpherson N, Nelson BH, Watson PH: Tumor-infiltrating lymphocytes predict response to anthracycline-based chemotherapy in estrogen receptor-negative breast cancer. Breast cancer research 2011, 13(6):R126.
  57. Mao Y, Qu Q, Chen X, Huang O, Wu J, Shen K: The prognostic value of tumor-infiltrating lymphocytes in breast cancer: a systematic review and meta-analysis. PloS one 2016, 11(4):e0152500.
  58. Mao Y, Qu Q, Zhang Y, Liu J, Shen K: Tumor infiltrating lymphocytes (TIL) to predict response to neoadjuvant chemotherapy in breast cancer: A systemic review and meta-analysis. Journal of Clinical Oncology Conference 2014, 32(26 SUPPL. 1).
  59. Carbognin L, Pilotto S, Nortilli R, Brunelli M, Nottegar A, Sperduti I, Giannarelli D, Bria E, Tortora G: Predictive and Prognostic Role of Tumor-Infiltrating Lymphocytes for Early Breast Cancer According to Disease Subtypes: Sensitivity Analysis of Randomized Trials in Adjuvant and Neoadjuvant Setting. The oncologist 2016, 21(3):283-291.