Association between oral contraceptive use as a risk factor and triple-negative breast cancer: A systematic review and meta-analysis.

Triple-negative breast cancer (TNBC), a unique subtype of breast cancer, which is resistant to endocrine and targeted therapy, usually relapses early, progresses rapidly and is associated with a poor prognosis. Epidemiological investigations focusing on the association between risk factors and the onset of TNBC demonstrated that the incidence of TNBC exhibits a significant correlation with anthropometric, geographical and demographic parameters. The aim of the present systematic review and meta-analysis was to evaluate the strength of the association between the use of oral contraceptives (OCs) and TNBC. Two databases (PubMed Central/PubMed, Web of Science) and secondary references were searched to identify studies meeting the priorly established inclusion criteria. Case-control studies published between January, 2005 and March, 2016 were searched using the key words (triple-negative breast cancer OR basal-like) AND (oral contraceptives). Finally, 9 eligible articles using as control other subtypes of invasive breast cancer and 7 articles using a healthy population as control were incorporated in the meta-analysis. Pooled odds ratio (OR) and 95% confidence interval (CI) were calculated using fixed- or random-effects models according to the heterogeneity between studies. The case-control comparison using other subtypes of breast cancer as the control arm exhibited a significant association between OC use and TNBC (OR = 1.31, 95% CI = 1.18-1.45; Z=5.26, P<0.00001). These results were further confirmed by the case-control comparison using the healthy population as the control arm (OR = 1.21, 95% CI = 1.01-1.46; Z=2.04, P=0.04). The present meta-analysis indicated that women who use OCs have a greater risk of TNBC compared with women who do not. This conclusion prompts that women who used OCs should be examined more closely in population screenings of breast cancer, as they may benefit from prevention and early detection strategies.