Circulating Tumor DNA is Unreliable to Detect Somatic Gene Alterations in Gastrointestinal Peritoneal Carcinomatosis
Brittany G. Sullivan, Angelina Lo, Jingjing Yu, Amber Gonda, Farideh Dehkordi‐Vakil, Farshid Dayyani, Maheswari Senthil
Abstract
INTRODUCTION: Tumor agnostic circulating tumor DNA (ctDNA) is routinely used to guide treatment decisions in gastrointestinal (GI) cancers, especially metastatic cancers. The amount of ctDNA detected in plasma is affected by stage, tumor burden, and tumor vascularization. We hypothesized that peritoneal carcinomatosis (PC) is associated with lower ctDNA levels than other metastatic sites in GI cancers due to the plasma-peritoneal barrier. METHODS: ). ctDNA analysis was performed on early and pretreatment samples. We compared the reported maximum variant allele frequency (mVAF) of somatic mutations across metastatic sites. RESULTS: Of the 279 patients with GI cancers (colorectal, upper GI, pancreaticobiliary), 212 had stage IV disease (PC: n = 61; visceral metastases: n = 138; other metastases: n = 13). Mean mVAF increased with increasing stages of disease (stage II: 3.6 ± 7; stage III: 6.4 ± 10; stage IV: 28.0 ± 51; p < 0.01). Among patients with stage IV disease, PC was associated with lower ctDNA levels independent of primary tumor site (PC only: 12.1%; PC+ visceral metastases: 26.8%; and visceral metastases only: 35.0%; p < 0.01). In a subset of patients (n = 27, matched pair analysis of genomic alterations (GAs) showed fewer GAs were detected in plasma compared with tissue. CONCLUSIONS: PC of GI origin is associated with significantly lower ctDNA levels compared with visceral metastasis. Caution is warranted when interpreting ctDNA results from patients with PC due to lower sensitivity for detecting actionable mutations.