Parity and kidney cancer risk: evidence from epidemiologic studies.

BACKGROUND Observational studies have reported conflicting results between parity and kidney cancer risk. To our knowledge, a comprehensive and quantitative assessment of the association between parity and kidney cancer has not been reported. Thus, we conducted a systematic review and dose-response meta-analysis of published epidemiologic studies to summarize the evidence of this association. METHODS Relevant published studies of parity and kidney cancer were identified using MEDLINE (PubMed) database through end of June 2013. Two authors independently assessed eligibility and extracted data. Six prospective and eight case-control studies reported relative risk (RR) estimates and 95% confidence intervals (CI) of kidney cancer associated with parity or parity number. Fixed- or random-effects models were used to estimate summary relative risk. RESULTS The summary relative risk of kidney cancer for the parity versus nulliparous was 1.23 (95% CI, 1.10-1.36; Q = 12.41; P = 0.413; I(2) = 3.3%). In addition, significant association was also found for the highest versus lowest parity number, with summary RR = 1.36 (95% CI, 1.19-1.56; Q = 8.24; P = 0.766; I(2) = 0%). In the dose-response analysis, the summary per one live birth relative risk was 1.08 (95% CI: 1.05-1.10; Q = 9.34; P = 0.500; I(2) = 0%), also indicating the positive effect of parity on kidney cancer risk. No evidence of publication bias and significant heterogeneity between subgroups was detected by meta-regression analyses. CONCLUSIONS In summary, findings from this meta-analysis suggest that ever parity and higher parity number is significantly associated with increased risk of kidney cancer. IMPACT The present results suggest a positive association between parity and kidney cancer risk.