PARP Inhibitor Efficacy in mCRPC with CHEK2 Mutations

Regulatory Approval and Guideline Recommendations

The National Comprehensive Cancer Network (NCCN) recommends olaparib for mCRPC patients with CHEK2 mutations who have progressed on prior androgen receptor-directed therapy, with a Category 1 recommendation 1, 3
The FDA approved olaparib for mCRPC patients with deleterious or suspected deleterious germline or somatic HRR gene mutations in 14 genes, including CHEK2, following progression on enzalutamide or abiraterone 1, 2

The PROfound trial demonstrated significant heterogeneity in PARP inhibitor response based on specific HRR gene mutations, with CHEK2 showing substantially less benefit than BRCA1/2 mutations 4
The trial reported a radiographic PFS HR of 0.34 (95% CI, 0.25-0.47; P<0.001) and OS HR of 0.69 (95% CI, 0.50-0.97; P=0.02) for Cohort A (BRCA1/2, ATM) 2, 4
CHEK2 was included in Cohort B, which failed to meet its primary endpoint for radiographic PFS benefit 3

Prior therapy requirement: Patient must have received prior enzalutamide or abiraterone 1, 2
Confirmed mutation: Use commercially available analytically and clinically validated somatic tumor, ctDNA, or germline assays 1, 3
Realistic expectations: Counsel patients that CHEK2 mutations show lower response rates than BRCA1/2 mutations 3, 4

Close monitoring with complete blood counts and hepatic/renal function is mandatory, with transfusion support and dose reductions as needed for severe anemia 1, 5
Common adverse events include anemia (20% grade 3/4), fatigue (12% grade 3/4), nausea, vomiting, anorexia, weight loss, diarrhea, and thrombocytopenia 1

The most critical pitfall is overestimating efficacy in CHEK2 carriers based on the overall PROfound trial results, which were driven by BRCA1/2 mutations 3, 4