ideasIdea
CDK4-selective inhibitors as the new first-line backbone
If a CDK4-only drug matches CDK4/6 inhibitors on efficacy with less neutropenia, continuous dosing and better adherence could translate into longer control.
Atirmociclib (Pfizer) and other CDK4-selective agents aim to remove the CDK6-driven neutropenia that forces dose holds and reductions with palbociclib, ribociclib, and abemaciclib.
Hypothesis
CDK4-selective inhibition + letrozole is non-inferior or superior in PFS to CDK4/6 + letrozole in first-line HR+/HER2- disease, with fewer grade 3+ haematologic events and higher relative dose intensity.
Rationale
Luminal breast cancer depends on cyclin D1-CDK4; CDK6 dependence is mainly haematopoietic. FOURLIGHT-1 showed activity after CDK4/6 failure.
What would test it
FOURLIGHT-3 phase 3 (enrolling); secondary analyses of dose intensity and quality of life.
Maturity
early clinical