Characterization of ctDNA findings at the end of life in patients with prostate cancer.

Abstract

230 Background: Somatic alterations change over time in response to treatment and disease progression in patients with prostate cancer (PCa). We report ctDNA findings of patients who died from PCa within 3 months of a ctDNA assessment to better characterize patients with fatal disease. Methods: A total of 118 patients with PCa specific mortality who had been treated at Tulane Cancer Center and had ctDNA assessments between 2015 and 2022. The ctDNA was assessed by Guardant360 (Guardent Health, Inc) assays to identify alterations, pathogenic mutations and/or copy number alterations (CNAs) in cancer-related genes. Clinical annotation including treatment history, genetics, and staging were also obtained. Statistical analyses included Fischer’s Exact and Wilcoxon tests. Results: Of the 118 patients with PCa specific mortality, 42% (49/118) had a ctDNA assessment <3 months from death. Of 49 CRPC patients tested within 3 months of death, the median number of life extending therapies (LET) at death was 5 (2-9). Patients had a median of 2 (0-6) LET prior to first ctDNA screening and 3 (0-7) LET in between first and last ctDNA assessment. Of the total gene alterations detected on ctDNA analysis, within 3 months of death, the most common alterations detected were 65.3% (32/49) TP53, 44.9% (22/49) AR, 28.6% (14/49) EGFR, 24.5% (12/49) PIK3CA, 22.4% (11/49) MYC, and 20.4% (10/49) CDK6. In a paired analysis(n= 45) of first and last ctDNA screening, AR (OR= 2.35, 95% C.I. (0.99, 5.62), p= 0.05), CDK6 (OR= 4.00, 95% C.I. (1.02, 15.68), p= 0.04), FGFR1 (OR= 9.51, 95% C.I. (1.14, 79.61), p= 0.03), and EGFR (OR= 9.71, 95% C.I. (2.06, 45.83), p= 0.0009) were significantly more likely to be detected in ctDNA screening within 3 months of death. In addition, ctDNA alterations in general were significantly more likely to be detected at the end-of-life (p=< 0.00001). Other ctDNA gene mutations did not have statistically significant increases. Conclusions: An analysis of patients with PCa mortality showed most frequent gene alterations in TP53, AR, EGFR, PIK3CA, MYC, and CDK6. When comparing patients’ first and last ctDNA, alterations were significantly more likely by time of death in AR, CDK6, EGFR, FGFR and there was a significant increase in overall detection of somatic alterations in ctDNA. These analyses are limited to the genes assessed on the ctDNA panel and may or may not reflect all of the functionally relevant alterations. Further the CNAs reported herein may reflect broad genomic changes rather than specific gene alterations.