Response evaluation with F-18-FDG PET/CT in metastatic breast cancer patients treated with Palbociclib: first experience in clinical practice

Objective: Palbociclib is a cyclin-dependent kinase 4/6 inhibitor recently approved for treatment in advanced or metastatic breast cancer (BC) patients. The use of 18 F-FDG PET/CT for chemo/endocrine therapy response assessment in BC patients is well reported in the literature, but no studies have evaluated its role for assessing Palbociclib efficacy in clinical practice. Our study aimed to evaluate the potential role of 18 F-FDG PET/CT in this setting. Methods: In 12 metastatic BC patients (mean age = 62 ± 10 years) treated with Palbociclib plus endocrine therapy and who underwent a baseline and post-therapy 18 F-FDG PET/CT, we retrospectively compared the Metabolic Response Evaluation (MRE, based on PET/CT) to the Standard Response Evaluation (SRE, based on clinico-laboratory and morphological data); we also assessed the influence of additional PET/CT information on the patients’ management. Results: Compared to SRE, MRE increased the proportion of patients classified with progressive disease from 25 to 50% and differed from SRE in 8/12 patients: 3/8 shifted from stable disease or undetermined response to metabolic progression (more unfavorable category), 4/8 from stable disease to partial or complete metabolic response, and 1/8 from partial response to complete metabolic response (more favorable category). Additional PET/CT information led to a change in patients’ management in 3/12 (25%) patients. Conclusion: In BC patients treated with Palbociclib, additional 18 F-FDG PET/CT information seems clinically useful, with respect to personalized management, to early intercept patients who should discontinue Palbociclib because of progressive disease and to select patients requiring a strict monitoring of additional metabolic findings. Further studies are needed to confirm these preliminary results