Emergence of PALB2 Reversion Mutations as a Mechanism of Resistance to Niraparib in Breast Cancer: A Case Report

This case study describes the clinical course of a 39-year-old woman with metastatic breast cancer harboring a germline PALB2 mutation who was treated with a PARP inhibitor. She initially demonstrated a clinical benefit with reduced tumor markers and favorable imaging findings. However, disease progression occurred after eight months. Liquid biopsy-based genomic profiling identified three PALB2 reversion mutations that restored homologous recombination, leading to treatment resistance. The case illustrates both the therapeutic potential of PARP inhibitors in PALB2-mutated cancers and the emergence of resistance. It emphasizes the importance of liquid biopsy-based genomic profiling for understanding tumor evolution and guiding treatment strategies.