Circumferential Resection Margin as Predictor of Non-clinical Complete Response in Nonoperative Management of Rectal Cancer

Dis Colon Rectum. 2023 Mar 6. doi: 10.1097/DCR.0000000000002654. Online ahead of print.

Abstract

Background: Short-course radiation therapy and consolidation chemotherapy with nonoperative intent has emerged as a novel treatment paradigm for patients with rectal cancer, but there are no data on the predictors of clinical complete response.

Objective: To evaluate the predictors of clinical complete response and survival.

Design: Retrospective cohort.

Settings: NCI-designated cancer center.

Patients: Stage I-III rectal adenocarcinoma treated between 01/2018 and 05/2019 (n = 86).

Interventions: Short-course radiation therapy followed by consolidation chemotherapy.

Main outcome measures: Logistic regression were performed to assess for predictors of clinical complete response. The endpoints included local regrowth-free survival, regional control, distant metastasis-free survival, and overall survival.

Results: A positive (+) circumferential resection margin by magnetic resonance imaging at diagnosis was a significant predictor of non-clinical complete response (odds ratio: 4.1, p = 0.009) when adjusting for carcinoembryonic antigen level and primary tumor size. Compared to patients with a negative (-) pathologic circumferential resection margin, patients with a positive (+) pathologic circumferential resection margin had inferior local regrowth-free survival (29% vs. 87%, p < 0.001), regional control (57% vs. 94%, p < 0.001), distant metastasis-free survival (43% vs. 95%, p < 0.001), and overall survival (86% vs. 95%, p < 0.001) at 2 years. However, the (+) and (-) circumferential resection margin by magnetic resonance imaging subgroups in patients who had a clinical complete response both had similar regional control, distant metastasis-free survival, and overall survival of >90% at 2 years.

Limitations: Retrospective design, modest sample size, short follow-up, and the heterogeneity of treatments.

Conclusions: Circumferential resection margin involvement by magnetic resonance imaging at diagnosis is a strong predictor of non-clinical complete response. However, patients who achieve a clinical complete response following short-course radiation therapy and consolidation chemotherapy with nonoperative intent have excellent clinical outcomes regardless of the initial circumferential resection margin status.