CDK4/6 inhibitors for HR+HER2− early stage breast cancer — when to escalate treatment?

Opposing results of the monarchE and PALLAS trials investigating the role of adjuvant treatment with the CDK4/6 inhibitors abemaciclib and palbociclib, respectively, in patients with hormone receptor-positive, HER2-negative early stage breast cancer have recently been presented. Herein, potential reasons why these two drugs that have similar efficacy in the metastatic setting have produced disparate results in the adjuvant setting are discussed.