Impact of somatic DNA repair mutations on bone-related efficacy endpoints in patients with metastatic castration-resistant prostate cancer (mCRPC): A retrospective analysis.

214 Background: Up to 80% of mCRPC have bone metastases and about 25% of metastatic prostate cancer harbor mutations in DNA damage repair defects (DDR). DDR gene mutations are a negative prognostic factor, being associated with short metastasis-free survival and cancer-specific survival. We analyzed the impact of somatic mutations in DDR genes on bone-related efficacy endpoints in mCRPC. Methods: We retrospectively analyzed the mutational status of mCRPC patients per FoundationOne analysis in tissue biopsy or, when it was not possible, in liquid biopsy (performed at the onset of mCRPC). We evaluated the impact of DDR gene mutations on bone-related efficacy endpoints at the time of mCRPC diagnoses, by dividing patients in two main groups (mutated DDR, specifically, mutations in at least one of BRCA1/2, ATM, FANCA, ATR, CHEK2, RAD51, PALB2, and CDK12 genes: group A; wild-type DDR: group B). We investigated differences between the two groups in terms of time from bone metastases onset to death, skeletal metastatic tumor burden (sites and number of lesions), skeletal-related events (SRE) incidence, and time to first on-study SRE. Results: Of the 131 patients with mCRPC enrolled, 115 had bone metastases. Clinical data distribution, according to molecular profile, is presented. There is no difference in terms of sites of metastases and time from bone metastases onset to death between the 2 groups. Mutated DDR status was associated with bone metastases volume (p = 0.0325), but did not affect SRE incidence and time to SRE onset. Conclusions: In our analysis, mutated DDR status was associated with higher bone metastases volume, although a not detrimental effect on the other bone-related efficacy endpoints was observed. [Table: see text]