Abstract 99P
Background
For patients with metastatic colorectal cancer (mCRC) with limited disease, systemic therapy and definitive locoregional therapy, including resection, radiotherapy, and ablation, can improve survival. In this study, we aim to investigate the utility of ctDNA as a prognostic marker in patients with mCRC undergoing systemic and locoregional therapy.
Methods
After approval by the institutional review board, we conducted a retrospective search at a hybrid academic-community cancer care network for patients with mCRC and limited metastatic burden who had tumor-informed ctDNA testing (Signatera) and received definitive therapy. We collected data on patient characteristics, disease characteristics, treatment details and survival by retrospective chart review. The primary endpoint of the analysis was disease-free survival (DFS) in patients with detectable ctDNA versus patients with negative ctDNA following treatment completion.
Results
Our study included 44 patients with a median age of 59 years (range 32-83). 23 (52.3%) patients were female, and the majority (70.5%) were white. 19 (43.2%) patients had RAS mutations, 28 (63.6%) had synchronous metastases, and 32 (72.7%) had left-sided primary tumors. The most common sites of metastasis were the liver (77.3%), followed by the lung (6.8%). The most common definitive therapy for metastatic disease was resection (64%), followed by radiotherapy (4%), and the rest underwent multimodal therapy (32%). The median duration of systemic chemotherapy was 12 weeks (range 0-56). Following definitive therapy, 20 (45%) patients were ctDNA positive, and 24 (55%) were ctDNA negative. The median DFS of patients with negative ctDNA was 18.4 months compared to 8.3 months in ctDNA positive patients (p=0.023). Amongst patients with negative ctDNA, adjuvant therapy was not significantly associated with improved DFS (p=0.852).
Conclusions
ctDNA testing has prognostic value in patients with mCRC undergoing definitive therapy. Ongoing prospective studies will define the role of ctDNA-guided therapy in this patient population.
Legal entity responsible for the study
The authors.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.