Molecular Phenotype of Breast Cancer According to Time Since Last Pregnancy in a Large Cohort of Young Women

Abstract

Background. The increase in breast cancer risk during pregnancy and postpartum is well known; however, the molecular phenotype of breast cancers occurring shortly after pregnancy has not been well studied. Given this, we investigated whether nulliparity and the time interval since pregnancy among parous women affects the breast cancer phenotype in young women. Materials and Methods.We examined molecular phenotype in relation to time since pregnancy in a prospective cohort of 707 young women (aged #40 years) with breast cancer. Parity wasascertained fromstudyquestionnaires. Usingtumor histologic grade on central review and biomarker expression, cancers were categorized as luminal A- or B-like, HER2 enriched, and triple negative. Results. Overall, 32% were luminal A-like, 41% were luminal B-like, 9% were HER2 enriched, and 18% were triple negative. Although, numerically, patients diagnosed .5 years after pregnancy had more luminal A-like subtypes thanwomenwith shorter intervals since pregnancy, there was no evidence of a relationship between these intervals and molecular subtypes once family history of breast cancer and age at diagnosis were considered. Conclusion. Distribution of breast cancer molecular phenotype did not differ significantly among young women by parity or time interval since parturition when important predictors of tumor phenotype such as age and family history were considered.