‘Inner world’ of luminal HER 2-negative metastatic breast cancer: Efficacy of ribociclib in different intrinsic subtypes

Abstract

The heterogeneity of breast cancer (BC), which determines various clinical scenarios of the disease, is still inaccessible to our understanding. Heterogeneity is based primarily on intrinsic subtypes of breast cancer, determined using genomic tests. Currently, four intrinsic subtypes are generally recognized: luminal A and B, HER-enriched (HER2-E) and basal-like. HER2-E subtype in luminal HER-negative (ER+HER–) breast cancer accounts for 11–22 per cent of cases. The efficacy of a combination of hormone therapy (HT) and the CDK4/6 inhibitor ribociclib in the HER2-E subtype was evaluated in a large exploratory analysis of MONALEESA-2, -3, and -7 trials. The gain in progression-free survival (PFS) and overall survival (OS) from the addition of ribociclib to HT was observed in all intrinsic subtypes, except for basal-like, and reached maximum in HER2-E subtype: Ribociclib increased the median PFS to 16.4 months from 5.5 months on HT (HR = 0.389; p < 0.0001) and median OS to 40.3 months from 29.4 months (HR = 0.600; p = 0.0180). The significant frequency of occurrence of the HER2-E subtype in ER+HER-BC, the low efficiency of monoHT in this subtype is another argument in favor of prescribing combination therapy in early lines. Information about the intrinsic subtype not only brings us closer to understanding tumor heterogeneity, but may also become a significant factor in determining treatment tactics in the future.