Variant allele frequency changes in TP53 predict pembrolizumab response in patients with metastatic urothelial carcinoma

Prognoses for patients with metastatic urothelial carcinoma (mUC) have improved with pembrolizumab treatment, an immune checkpoint inhibitor, but clinical benefits are limited to a subset of patients. Therefore, a non-invasive biomarker to predict pembrolizumab response is required. The present study retrospectively examined genomic alterations in 25 plasma circulating tumor DNA (ctDNA) samples using targeted sequencing of 77 genes from 16 patients with mUC during pembrolizumab treatment. A total of 11 (68.8%) patients demonstrated ≥2 genomic alterations, including TP53 mutations (as defined by ctDNA-positive status). The proportion of responders to pembrolizumab in the ctDNA-positive group was higher compared with that in the ctDNA-negative group (72.7 vs. 20.0%). Furthermore, among all detected genomic alterations, variant allele frequency decreases in TP53 during pembrolizumab treatment were mainly associated with therapeutic response. Collectively, these data suggest that profiling of ctDNA in plasma, particularly TP53, may be useful for predicting and monitoring therapeutic responses to pembrolizumab in patients with mUC.