Baseline genomic and circulating tumor cell (CTC) correlative data from very high-risk (VHR), localized, node-negative prostate cancer patients.

Abstract

e16563 Background: Few data exist on CTC frequency and number, genetic landscape, and tumor mutational burden (TMB) in VHR, node negative, localized prostate cancer (PCa). Methods: We are conducting a single-arm phase 2 trial of ultra-hypofractionated radiation (RT) with 6 months of abiraterone, apalutamide and leuprolide in VHR PCa, defined as: Gleason (Gl) 9-10 or 2 high risk features (including radiographic (r) T3/T4 disease) or > 4 cores of Gl8. We report baseline correlatives in the first 38 screened patients (pts). CTCs were isolated using a non-selection based platform (EPIC Sciences). Additional analyses were conducted using MSK IMPACT, a next generation sequencing assay. Results: Median PSA was 14.8 ng/mL (IQR, 7.7-28.1); Gl7 was present in 5% (n = 2), Gl8 in 32% (n = 12), Gl9 in 61% (n = 23) and Gl10 in 2% (n = 1) of pts; on MR, 42% of pts were rT2 (n = 16), 39% had rT3a disease (n = 15) and 18% had rT3b disease (n = 7). CTC data were available on 31 pts; 74% (n = 23) had ≥1 detectable CTC (range, 0.8-14.6 cells per mL); 29% (n = 9) had CK+ clusters (range, 0.8-7.1 clusters per mL). IMPACT was available for 20 pts: KMT2D/C mutations were present in 25% (n = 4), TP53 missense mutations in 20% (n = 4), FOXA1 mutations in 20% (n = 4), PTEN truncating or missense mutations in 15% (n = 3), SPOP missense mutations in 15% (n = 3), PIK3CA activating mutations in 15% (n = 3), APC deletions in 15% (n = 3); 85% (17/20) had alterations in one of these genes. No clinically significant germline mutations were present. Median TMB was 2.63 mutations/mB (range, 0.87-60.56); the TMB-highest pt had an in-frame deletion in MSH2. Among IMPACTed pts with normalized testosterone post-protocol treatment (n = 16), there was a trend towards an association with SPOP/FOXA1 mutations and undetectable ( < 0.05 ng/mL) PSA; 5/6 pts with mutations had undetectable PSA (83.3%) vs 3/10 without (30%) (p = 0.12). The trial is managed by the PCCTC and funded by Janssen. Conclusions: The genetic profile and TMB of VHR, localized PCa resembles non-castrate, metastatic disease. The frequency of detectable CTCs is high with implications for post-treatment surveillance. SPOP/FOXA1 mutations may predict initial response to RT with total androgen blockade. Clinical trial information: NCT02772588.