CDK12 Loss in Prostate Cancer Imparts Poor Prognosis and Limited Susceptibility to Immune Checkpoint Inhibition

Abstract

191Background: Translational studies have shown that CDK12 mutations may delineate an immunoresponsive subgroup of PC, characterized by high neoantigen burden. Given that these mutations may define a clinically relevant PC subgroup, we sought to describe outcomes to both standard drugs and PD1 inhibitors. Methods: Clinical data from consecutive patients with CDK12 mutations were retrospectively collected from 7 centers. Multiple clinical grade sequencing assays were used to assess for CDK12 alterations. Descriptive statistics included PSA50 (≥50% decline in PSA from baseline) and clinical/radiographic progression-free survival (PFS). Results: Of 56 CDK12-mutated PC patients, 27 (48%) had biallelic CDK12 alterations. At diagnosis, 46 (82%) had Gleason grade group 4-5 disease, 52% had T3-T4 disease and 15 (27%) had M1 disease. Median follow up was 8.2 yrs (95% CI: 5.6-11.1) and 53 (95%) developed metastatic disease. Median overall survival (OS) from metastasis was 3.9 years (95% CI: 3.2-5.8). Nineteen patients received an anti-PD1 therapy. PSA50 responses to PD1 blockade were infrequent and overall PFS was short (Table); however, the estimated 9-month PFS was 23%. PFS was higher in chemotherapy naïve patients who received anti-PD1 therapy (P=0.004). Outcomes were similar in monoallelic vs. biallelic CDK12-mutated patients. Conclusions: CDK12-mutations define an aggressive PC subgroup, with a high rate of metastatic disease and short OS. Immune checkpoint inhibitors may be effective in a minority of these patients and exploratory analysis supports using anti-PD1 drugs early.[Table: see text]