Palbociclib in solid tumor patients with genomic alterations in the cyclin D-CDK4/6-INK4a-Rb pathway: Results from NCI-COG pediatric MATCH trial Arm I (APEC1621I).
Authors: Macy Margaret E , Mody Rajen , Reid Joel M. , Piao Jin , Saguilig Lauren , Alonzo Todd Allen , Berg Stacey L. , Fox Elizabeth , Hawkins Douglas S. , Mooney Margaret M. , Williams P. Mickey , Patton David R. , Coffey Brent D. , Roy-Chowdhuri Sinchita , Takebe Naoko , Tricoli James V. , Janeway Katherine A. , Seibel Nita , Parsons Donald Williams 
Published: June 2023

10006 Background: The NCI-Children’s Oncology Group (COG) Pediatric Molecular Analysis for Therapy Choice (MATCH) trial assigns patients aged 1 to 21 years with relapsed or refractory solid tumors, lymphomas, and histiocytic disorders to phase 2 treatment arms of molecularly-targeted therapies based on genetic alterations detected in their tumor. Arm I evaluated palbociclib, a reversible, selective oral small molecule inhibitor of CDK 4 and 6 in tumors harboring specified genomic alterations in the cyclinD-cdk4/6-INK4a-Rb pathway: amplification of CDK4, CDK6, CCND1, CCND2, or CCND3. Positive Rb expression by IHC was required. Methods: Palbociclib was administered on days 1-21 at 75 mg/m2 once daily in 28-day cycles for up to 2 years, until disease progression, or intolerable toxicity. Response assessment occurred every 2-3 cycles. The primary endpoint was objective response (OR) rate; secondary endpoints included safety/tolerability and progression-free survival (PFS). Results: Twenty-three patients (median age 15 yrs; range 9-21) were enrolled between August 2018 and May 2022. Twenty patients received protocol therapy and were evaluable for response. Of treated patients, osteosarcoma was the most common diagnosis (9/20, 45%), with amplification of CCND3 detected in 6/9 patients, CDK4 in 2, and CDK6 in 1. Rhabdomyosarcoma was next most frequent (6/20, 30%), with all tumors harboring CDK4 amplifications. Other diagnoses were high grade glioma (n = 2), soft tissue sarcoma (n = 2), and neuroblastoma (NB) (n = 1). Additional genomic alterations were detected in 9/20 tumors, most frequently TP53 mutations (n = 4, including 2 patients with Li-Fraumeni syndrome). Palbociclib was generally well tolerated with hematologic toxicities being the most common treatment related events and no related grade 5 events. Neutropenia was the most common grade 3-4 adverse event (n = 10, 50%) followed by thrombocytopenia (n = 8, 40%), leukopenia (n = 7, 35%), and anemia (n = 5, 25%). Four patients came off study for toxicity (3 for prolonged thrombocytopenia (cycle 1 (x2) and cycle 2) and 1 for prolonged grade 4 neutropenia (cycle 3)). Non-hematologic toxicities were mild (grade 1-2). No ORs were seen. Two patients with tumors harboring CDK4 amplifications had stable disease (SD): one with NB had SD for 5 cycles and one with sarcoma had SD for 3 cycles but came off therapy for toxicity. Six-month PFS was 10% (95% CI: 1.7%-27.2%) and six-month overall survival was 65% (95% CI: 40.3%, 81.5%). Conclusions: The CDK4/6 inhibitor palbociclib at 75mg/m2 PO daily was well tolerated in this heavily-pretreated cohort. No objective responses were observed in these biomarker-selected patients with treatment-refractory solid tumors. Further evaluation of this agent in combination with chemotherapy in the pediatric population is ongoing. Clinical trial information: NCT03526250 .