Clonal hematopoiesis of indeterminate potential (CHIP) and association with response to bipolar androgen therapy (BAT)

e17048 Background: CHIP, the expansion of hematopoietic cells carrying acquired somatic alterations associated with hematologic malignancies, is associated with increased inflammation, risk of heart disease, and poor outcomes. BAT, where testosterone levels are therapeutically manipulated between castrate levels to supraphysiologic levels, has been shown to be an effective therapy for some men with castration resistant prostate cancer. Clinical predictors of response are not established. We hypothesized that CHIP, would be negatively associated with clinical outcomes. Methods: Baseline peripheral blood from participants on the RESTORE Cohort C (NCT02090114) were analyzed for the presence of CHIP. Patients in this cohort had castration resistant prostate cancer with progressive disease after treatment with ADT alone. All participants were treated with 400mg of intramuscular testosterone cypionate every 28 days. Peripheral blood mononuclear cells were analyzed for the presence of CHIP using targeted next generation sequencing focused on 49 genes most commonly mutated in CHIP and myeloid malignancies. Given patients had metastatic and non-metastatic CRPC, progression free survival was determined based on the time to the start of the next therapy. Results: CHIP was present in 6 of 29 patients at baseline (21%) with one patient having 2 clones (Table). Median age of patients CHIP+ was 73 compared to age of 68 in the CHIP- group (p = 0.16). Median PSA was higher in the CHIP+ group (median 15, IQR 1-56) compared to the CHIP- group (median 3.5, IQR 1-57). 67% of the CHIP+ group and 57% of the CHIP- group had baseline Gleason scores of > = 8. The CHIP+ group had a median PFS of 8.8 months compared to 13.3 months in the CHIP- group (HR 3.3 95%CI 1.2, 9.1; p = 0.02). This remained significant after adjusting for age. There was no difference in overall survival (HR = 2.5 95% CI 0.5,2.9; p = 0.3). Conclusions: Among men treated with BAT as first line treatment for CRPC after ADT alone, CHIP was associated with a decreased progression free survival. Larger studies are needed to understand the impact of CHIP in larger cohorts of men treated with BAT and other therapies for prostate cancer.[Table: see text]