Introduction
tumor, Tumor, cancer, heterogenous aggressive malignancy, Cancer
TUMOR, TUMOR, CANCER, PRIMARY TUMOR, CANCER
Cancer of unknown primary (CUP) is a heterogenous aggressive malignancy characterized by histologically confirmed metastatic spread in the absence of a primary tumor responsible for metastatic seedingImmune checkpoint inhibitors (ICI) have evolved into indispensable components of the standard therapy for several cancer entities. However, since only a minority of patients derive durable benefit from ICI treatment, the need for robust predictors of response is immense. Tumor mutational burden (TMB) has emerged as an independent predictive biomarker of ICI efficacy. Based on the results of the KEYNOTE-158 study linking high TMB (TMBGiven the aggressive nature of unfavorable CUP, reliable early-on monitoring of therapeutic response is instrumental. The noninvasive longitudinal analysis of circulating cell free DNA (ccfDNA) and its tumor-derived fraction (ctDNA) has gained significant attention for this purpose, with its clinical utility currently being investigated in several tumor entitiesWe here report the results of the CheCUP trial, a multicenter phase II study of combined nivolumab (PD-1 checkpoint inhibitor) and ipilimumab (CTLA-4 checkpoint inhibitor) in patients with unfavorable CUP relapsed after or refractory to platinum-based chemotherapy (NCT04131621, EudraCT No. 2018-004562-33). Combined ultra-deep targeted next-generation sequencing (NGS) of patient-specific hotspot mutations and copy number alteration (CNA) profiling by low-coverage, shallow whole genome sequencing (sWGS) of ccfDNA from serial plasma samples was used to evaluate response to ICI treatment and compared to radiologic response assessment and survival. We find that 60% of CUP patients with high TMB respond to combined ICI therapy, with early on-treatment ctDNA analysis reliably identifying patients deriving long-term treatment benefit.