Using Tumor-Informed Circulating Tumor DNA (ctDNA)-Based Testing for Patients with Anal Squamous Cell Carcinoma

Background: Anal squamous cell carcinoma (SCCA) is an uncommon malignancy with a rising incidence that has a high cure rate in its early stages. There is an unmet need for a reliable method to monitor response to treatment and assist in surveillance. Circulating tumor DNA (ctDNA) testing has shown great promise in other solid tumors for monitoring disease progression and detecting relapse in real time. This study aimed to determine the feasibility and use of personalized and tumor-informed ctDNA testing in SCCA. Patients and Methods: We analyzed real-world data from 251 patients (817 plasma samples) with stages I-IV SCCA, collected between 11/5/19 and 5/31/22. The tumor genomic landscape and feasibility of ctDNA testing was examined for all patients. The prognostic value of longitudinal ctDNA testing was assessed in patients with clinical follow-up (N = 37). Results: Whole-exome sequencing analysis revealed PIK3CA as the most commonly mutated gene, and no associations between mutations and stage. Anytime ctDNA positivity and higher ctDNA levels (MTM/mL) were associated with metastatic disease (P =. 004). For 37 patients with clinical follow-up, median follow-up time was 21.0 months (range: 4.1-67.3) post-diagnosis. For patients with stages I-III disease, anytime ctDNA-positivity after definitive treatment was associated with reduced DFS (HR: 28.0; P =. 005). Conclusions: Our study demonstrates the feasibility of personalized and tumor-informed ctDNA testing as an adjunctive tool in patients with SCCA as well as potential use for detection of molecular/minuteimal residual disease, and relapse during surveillance. Prospective studies are needed to better evaluate the use of ctDNA testing in this indication.