Age-Specific Changes in Intrinsic Breast Cancer Subtypes: A Focus on Older Women

Abstract

©AlphaMed Press 2014. Purpose: Breast cancer (BC) is a disease of aging and the number of older BC patients in the U.S. is rising. Immunohistochemical data show that with increasing age, the incidence of hormone receptor-positive tumors increases, whereas the incidence of triple-negative tumors decreases. Few data exist on the frequency of molecular subtypes in older women. Here, we characterize the incidence and outcomes of BC patients by molecular subtypes and age. Patients and Methods: Data from 3,947 patients were pooled frompublicly available clinical and gene expression microarray data sets. The PAM50 algorithm was used to classify tumors into five BC intrinsic subtypes: luminal A, luminal B, HER2- enriched, basal-like, and normal-like. The association of age and subtype with recurrence-freesurvival (RFS), overall survival, and disease-specific survival (DSS) was assessed.Results: The incidence of luminal (A, B, and A+B) tumors increased with age (p <01, p <0001, and p <0001, respectively), whereas the percentage of basal-like tumors decreased (p <0001). Among patients 70 years and older, luminal B, HER2-enriched, and basal-like tumors were found at afrequency of 32%, 11%, and 9%, respectively. In olderwomen, luminal subtypes had better outcomes than basal-like and HER2-enriched subtypes. After controlling for subtype, treatment, tumor size, nodal status, and grade, increasingage had no impact on RFS or DSS. Conclusion: More favorable BC subtypes increasewith age, but older patients still have a substantial percentage of high-risk tumor subtypes. After accounting for tumor subtypes, age at diagnosis is notan independent prognostic factor for outcome.