Data sources and searches
A comprehensive literature search was performed of databases including PubMed, Cochrane Library, EMBASE, Web of Science, and SCOPUS to identify relevant studies up to December 1st, 2019. The following terms and their combinations were employed: (("prostate cancer") AND ("intraductal carcinoma")) OR ("IDC-P") OR ("intraductal carcinoma of the prostate") OR ("intraductal carcinoma of prostate").
Study selection
Every study was independently examined by two reviewers (Guoliang Sun and Yucong Zhang) for comprehensive evaluation according to the following inclusion criteria: (1) Patients were confirmed prostate cancer by pathological examination; (2) IDC-P was identified in prostate cancer tissues and was divided into present and absent categories; (3) studies investigated the association between IDC-P with clinicopathological features or prognosis; (4) studies directly provided HR with corresponding 95% CI, or survival curves of patients to estimate them; (5) studies were published in English. The exclusion criteria were as follows: (1) case reports, letters, reviews, editorials, notes, meeting abstracts, etc.; (2) non-human studies or in vitro studies; (3) duplicated studies with overlapping data; (4) studies provided information unable to be pooled.
Data extraction
Two authors (Chao Wei, Haojie Shang) independently extracted and summarized the data of interest, and disagreement was resolved by discussion. The following basic characteristics were collected: name of the first author, year of publication, country, tumor type, treatment, number of patients, age, Gleason score, tumor stage, nodal status, PSA, follow-up months. For survival data, IDC-P present or absent status with HR and 95% CI for PFS, CSS and OS were collected. The following clinicopathological data were extracted: numbers of IDC-P present and absent patients with (a) PSA values, (b) tumor stage cT1-cT2, (c) tumor stage cT3-cT4, (d) Gleason score≥8, (e) Gleason score <8, (f) lymph node metastasis N0, (g) lymph node metastasis N1, (h) positive surgical margins (i) negative surgical margins (j) positive extraprostatic extension, (k) negative extraprostatic extension.
Population, Interventions, Comparators, Outcomes and Study Designs (PICOS)
The population of our study is prostate cancer patients. IDC-P status was assessed in these patients. IDC-P present or absent were compared by the endpoint including PFS, CSS and OS. The associations between IDC-P status and clinicopathological characteristics were evaluated. The study was designed to evaluate the association between IDC-P status and prognosis and clinicopathological characteristics.
Quality assessment
Quality assessment was performed by two investigators (Zhuo Liu, Rui Li) independently according to the Newcastle-Ottawa Scale (NOS) criteria.[10] The NOS criteria consists of the following three parameters of quality: (1) selection: 0–4; (2) comparability: 0–2; and (3) exposure/outcome: 0–3.[10] Studies scoring greater than five were considered to be of high quality.
Data synthesis and analysis
HR with their 95% CI was used to estimate the association between PFS, CSS and OS and IDC-P status. Patients were dichotomized by tumor stage (cT1-T2 vs. cT3-T4), Gleason score (<8 vs.≥8), lymph node metastasis (N0 vs. N1), surgical margins (positive vs. negative), and extraprostatic extension (positive vs. negative) categories. OR with 95% CI was used to evaluate the correlation between IDC-P status and clinicopathological features. We used the Review Manager software version 5.3 to calculate HR and OR with 95% CIs. Heterogeneity was assessed by the Chi-squared test and I2 statistic. Fixed-effect models were employed when P-values of Chi-squared test is more than or equal to 0.05, and random-effect models when less than 0.05. Statistical tests were two-sided and P-values < 0.05 was considered to be statistically significant. Publication bias was assessed by funnel plots if number of included cohorts was over or equal to 10.