The combination of letrozole and trastuzumab as first or second-line biological therapy produces durable responses in a subset of HER2 positive and ER positive advanced breast cancers

Abstract

Estrogen receptor (ER) and/or progesterone receptor expression occurs in ∼50% HER2 positive (HER2+) breast cancers and cross-talk between the estrogen and HER2 pathways promotes endocrine therapy resistance. The efficacy of the aromatase inhibitor letrozole in combination with trastuzumab was therefore tested in a Phase 2 study.