High-Grade Neutropenia Marks Palbociclib Benefit in Early HR-Positive Breast Cancer

In PALLAS (N = 5,736 stage II–III HR+/HER2- cases), adding the CDK4/6 inhibitor palbociclib to adjuvant endocrine therapy (ET) failed overall, but an exploratory look at the 2,840 palbo-treated patients showed that those who developed grade ≥ 3 neutropenia within the first six cycles (HGN, 65%) experienced a 5-year invasive DFS of 85.6% versus 83.4% with ET alone (p = 0.04 after adjustment for BMI, prior chemo, and race). Patients with only low-grade/no neutropenia derived no benefit. HGN was more common in women with lower BMI, prior chemotherapy, Asian ancestry, and prior mastectomy; serious infections remained rare.