Which patients with estrogen receptor-positive early breast cancer should be treated with adjuvant chemotherapy?

Estrogen receptor expression in breast cancer cells represents an important predictive and prognostic factor. The estrogen receptor is a target for endocrine therapy, which avoids chemotherapy especially in highly hormone-sensitive early breast cancer. Paradoxically, recent data from several clinical trials and meta-analyses have demonstrated the superiority of adjuvant chemotherapy independently of age, estrogen receptor and nodal status. For this reason, new tools are needed to better define the intrinsic characteristics of breast cancers and to establish the role of cytotoxic treatment for those tumors with potentially good outcome, such as hormone-sensitive early breast cancer.