Clinical Benefit and Safety of Palbociclib in Hormone Positive Breast Cancer with Visceral Metastasis: Real-World Experience from a Tertiary Cancer Center

Abstract Introduction Palbociclib, the first CDK4/6 inhibitor, has shown promising results in phase III clinical studies by enhancing the efficacy of endocrine therapy (ET) in HR +/HER2– advanced breast cancer. However, real-world data on its use in patients with visceral metastatic disease are limited. We aimed to assess the effectiveness and tolerability of palbociclib in this high-risk population across different lines of treatment. Materials and Methods Patients with hormone-positive metastatic breast cancer who received palbociclib with ET between 2015 and 2021 were grouped into skeletal and visceral metastatic disease. Visceral metastatic diseases were subclassified into lung, liver, and brain metastatic diseases. All subgroups were analyzed for progression-free survival (PFS), toxicity, and prognostic factors. Subgroups were compared using the chi-square test, and survival analyses were done using the Kaplan–Meier test. Results Among 100 patients who received palbociclib, 70 had progressed on previous ET. The common metastatic site was bone (56%), followed by lung (24%), liver (18%), and brain (2%). With a median follow-up of 37 months, the median PFS of the overall population was 24 months: bone metastasis 27 months, lung 25 months, liver 12 months, and brain 4 months. Weak hormone positivity, ET-resistant metastatic patients, and high grade were associated with poorer responses. The common side effects were neutropenia (40%), anemia (35%), thrombocytopenia (15%), and hepatotoxicity (10%). Three percent of patients discontinued treatment due to toxicity. Conclusion Palbociclib with ET showed improved PFS and safety in visceral metastatic disease, comparable to randomized controlled trials. However, further studies are required to evaluate its efficacy in extensive visceral metastatic disease and previously heavily treated patients.