Breast cancer is a heterogeneous disease that comprises multiple molecular subtypes. In this study, there was no significant difference in tumor subtypes between FBC and NFBC patients (Table 1). Since Perou et al. used cDNA microarrays and performed gene expression profiling (GEP) of breast cancer in 2000, intrinsic subtype classification based on GEP has attracted attention [19, 20]. With this classification, breast cancer is divided into different subtypes of biologic properties such as luminal A, luminal B, HER2-enriched, basal-like, and normal breast-like. Because the prognosis and drug sensitivity vary according to subtype, it could become the index for choosing pharmacotherapy, but performing GEP in all cases of breast cancer is not realistic in a clinic. Therefore, in the Sankt Gallen consensus meeting of 2011 and 2013, a substitute definition of intrinsic subtype based on the ER/PgR/HER2/Ki67 status, mainly composed of immunohistochemical examinations performed as part of common pathological examinations, was adopted [21-23].
For the definitions of subtypes, Table 1 includes ER-/PgR-/HER2- triple negative breast cancer (TNBC), ER-/PgR-/HER2+, ER+/PgR+/HER2+, ER+and/orPgR+/HER2-, Luminal A-like (high ER/PR and clearly low Ki-67 or grade), and Luminal B-like (lower ER/PR with a clearly high Ki-67, histological grade 3 in the clinical grouping) [24]. HER2-enriched and the basal-like subtype should be defined only by genetic analysis, but this is not done. In the latest report, the exact counting method performed with a light-microscope showed the predictive value of Ki-67 assessment with a 10% cut-off value [25]. In the present study, prognostic factors were evaluated with new subtype according to stage, but a prognostic factor with a significant difference was not identified because the number of FBC patients was small.
In several malignancies, serum sIL-2R levels are higher than in healthy individuals. Although sIL-2R is not organ-specific, except for malignant lymphoma, measuring its serum level was shown to be valuable for stage evaluation and monitoring during treatment [26]. Breast cancer patients have been shown to have increased serum levels of sIL-2R [27], as well as IL-10, VEGF, IL-17, Treg, and MDSC [28-32]. Others have reported the correlations of sIL-2R in cancer with IL-10, VEGF, and IL-17, and the relationship between Tregs and MDSCs [33-35].
Consistent with the previously reported results, the results of the present study showed increased sIL-2R levels in all breast cancer patients compared with levels in healthy subjects. Overall, sIL-2R level was significantly higher in FBC than in NFBC. Compared with NFBC, FBC comprises cancer cells that contain more mutations, release neoantigens and have CD8+ T cells in and around the microenvironment that express IL-2 receptors and release more sIL-2Rs in blood. Moreover, in FBC, there are simultaneous increases in the level of IL-10 and the number of anti-immunologic suppressor cells, such as Tregs and MDSCs. In the present study, sIL-2R level in FBC patients was significantly and positively correlated with IL-10, VEGF, IL-17, Tregs, and MDSCs. In particular, the significant positive correlation of the sIL-2R level with IL-10 indicated disruption of the Th2>Th1 balance, which leads to Th2 predominance and suppression of cellular immunity. The significant positive correlations of the sIL-2R level with VEGF and IL-17 suggested further tumor development. The high levels of both VEGF and IL-17 further increased the number of cancer immunosuppressive cells. On the other hand, the present results showed no significant, positive correlations of sIL-2R with IL-10, VEGF, IL-17, Tregs, or MDSCs in NFBC patients. These results suggested very more dramatic inflammatory and immune responses in the cancer microenvironment of FBC than of NFBC.
High sIL-2R significantly increased the Tregs and MDSCs in FBC patients, but not in NFBC patients. This result implies the importance of preventing the growth of cancer immunosuppressive cells, such as Tregs and MDSCs, in FBC patients. Moreover, high sIL-2R indicated a significantly worse prognosis in FBC than in NFBC. The elevated sIL-2R level may have predisposed the FBC patients to cancer growth rather than cancer suppression. Notably, proliferation of CTLs does not guarantee the removal of all cancer cells. IL-2 is a systemically administered treatment that can lead to serious side effects, but decreasing its dose may render it ineffective [36, 37].
PD-L1 is expressed in 20% of TNBCs, suggesting PD-L1 as a therapeutic target in TNBCs. Because PTEN loss is one mechanism regulating PD-L1 expression, agents targeting the PI3K pathway may increase the antitumor adaptive immune responses [38]. In this study, immunohistochemical analysis confirmed tissue expressions of PD-L1 and CD8 in FBC with high sIL-2R and less CD8 staining in NFBC. These results indicated similar expressions of PD-LI in both FBC and NFBC, but, in the cancer microenvironment of FBC, Th2>Th1 balance occurred, because NLR, WBC, CRP, and IL-10, which are indices of inflammation, showed positive correlations. Furthermore, Tregs and MDSCs as anti-immunologic suppressor cells were present. Therefore, in and around the microenvironment, more CD8+ T cells seems to be induced and developed to attack a cancer. Although the direct relationship between IL-2 and PD-L1 is unknown, a combination of IL-2 and PD-L1 inhibitors has been the treatment regimen for chronic infections and cancer [39]. The duration of the proliferative contact between CD8+ T cells and antigen-presenting cells is affected by the sensitivity of individual CD8+ T cells to activation signals and by the concentration of IL-2 in the extracellular environment [40]. Regardless of the level of Tregs or MDSCs, immune checkpoint inhibitors should be effective, as long as CD8+ T cells proliferate. In the treatment of FBC patients, we should take into account the relationships between cancer and immunity, as well between cancer and genetics. In the future, shifting the Th1/Th2 balance towards Th1-dominant to inactivate cancer immunosuppressive cells may enhance the treatment efficacy of immune checkpoint inhibitors for patients with FBC.