Relationships between Reproductive Risk Factors for Breast Cancer and Tumor Molecular Subtypes

Background: Due to wide clinical differences in the various pathological types of breast cancer and also closeassociations between disease prognosis and molecular subtypes, relationships of the latter with traditional risk factorshave been suggested. Hence, the present study aimed to assess any associations. Methods: This bi-center cross-sectionalstudy was performed on 800 consecutive women with known breast cancer referred to two Comprehensive Cancer Centersin Tehran between 2006 and 2016. Baseline information related to reproductive risk profiles as well as pathologicaltumor diagnosis and molecular subtypes determined using immunohistochemical analysis by immune-staining forER, PR, and HER2 molecules were collected by reviewing hospital records. Results: Of 800 samples included forimmunohistochemical analysis, 314 (39.3%) were diagnosed as of Luminal A subtype, 107 (13.4%) as Luminal Bsubtype, 153 (19.1%) as HER-2 over-expressing, and 226 (28.3%) as triple negative. Among all reproductive riskfactors initially assessed, young age was associated with HER-2 over-expression, greater tumor size and a history ofabortion with the luminal B subtype, lower age at pregnancy with the luminal A subtype, and lower gravidity anda shorter duration of breastfeeding with the triple negative subtype. Conclusion: Each molecular subtype of breastcancer in our population may be associated with specific reproductive risk factors.