Relationship Among DNA Damage Response Gene Alterations, Molecular Subtypes, and Survival Outcomes in Patients With Metastatic Bladder Cancer Treated on CALGB 90601.

PURPOSE

In urothelial carcinoma, prior studies have indicated that the basal/squamous molecular subtype and the presence of select DNA damage response (DDR) gene alterations are associated with improved benefit from cisplatin-based chemotherapy. We sought to evaluate these biomarkers in specimens from the phase III Cancer and Leukemia Group B (CALGB) 90601 trial.

METHODS

We performed whole-transcriptome sequencing (n = 188) and exon capture DNA sequencing (n = 208) on pretreatment tumors from the CALGB 90601 randomized trial of gemcitabine/cisplatin plus bevacizumab or placebo in patients with treatment-naïve metastatic bladder cancer. Whole-exome sequencing (WES) was performed on tumors from 22 patients who exhibited rapid progression or durable response. Tumors were assigned to molecular subtypes using three different classifiers. Proportional hazards model was used to correlate molecular subtype with overall survival (OS) and progression-free survival (PFS), adjusting for stratification factors and treatment arm (for PFS).

RESULTS

Patients with basal tumors had the shortest PFS and OS in the entire cohort. PFS was numerically longer in patients with basal tumors receiving bevacizumab. DDR gene alterations were not associated with improved outcomes. , a candidate predictive biomarker of chemosensitivity identified by WES, did not confer sensitivity to cisplatin or gemcitabine in functional studies.

CONCLUSION

Molecular subtype and DDR alterations did not correlate with improved outcomes in CALGB 90601. Possible explanations for these results include the small cohort size, lack of strong therapeutic effects of the treatments, genomic heterogeneity between profiled specimens and the metastatic lesions under treatment pressure, and differences in biology associated with different disease states (muscle-invasive metastatic disease).