230P Early metabolic response by FDG-PET scan predicts survival in patients with metastatic breast cancer receiving CDK4/6 inhibitors: Preliminary results from the PUCCINI study

No reliable biomarkers exist to predict response to CDK4/6 inhibitors (CDK4/6i) in patients (pts) with metastatic breast cancer (MBC). FDG-PET scan, thanks to its sensitivity in detecting early metabolic changes in the tumour, could identify pts who will benefit from CDK4/6i. PUCCINI (PET evalUation in advanced breast Cancer treated with Cdk 4/6 INhIbitors) is a retrospective study conducted at Institut Jules Bordet evaluating the association between metabolic response by FDG-PET scan (assessed by PERCIST and CONSIST criteria) and survival (progression-free survival [PFS], overall survival [OS]) in pts with hormone receptor-positive, HER2-negative MBC receiving CDK4/6i and endocrine therapy (ET). FDG-PET scans were performed at baseline (i.e., before starting therapy) and at the first disease re-evaluation (i.e., 90 ± 15 days after starting therapy). Responders were defined as pts achieving a complete or partial (by PERCIST) or class I (by CONSIST) metabolic response. In this preliminary analysis, survival was estimated with the Kaplan-Meier method and compared by the log rank test and Cox proportional hazard models. This preliminary analysis was conducted on 28 eligible pts. After a median follow-up of 38.5 months (95% CI 35.9-41.1), we observed 18 disease progressions and 7 deaths. FDG-PET scans were evaluable by CONSIST and PERCIST in 24 patients. Metabolic response both by PERCIST and by CONSIST were significantly associated with longer PFS (Table). OS data are still immature (not presented).Table: 230PCONSIST (n=24)PERCIST (n=24)PFS events / Total NmPFS (months)HR (95% CI)PFS events / Total NmPFS (months)HR (95% CI)Responders8/18NR0.20 (0.06-0.64)10/2033.30.16 (0.05-0.55)Non-responders6/67.04/45.7HR: hazard ratio, NR: not reached. Open table in a new tab HR: hazard ratio, NR: not reached. Early metabolic response by FDG-PET scan in pts with MBC receiving CDK4/6i and ET is associated with longer PFS. Assessment of early metabolic response by FDG-PET scan is a promising strategy to identify pts who will benefit from CDK4/6i. More mature data on a larger cohort from the PUCCINI study will provide stronger evidence.