SCOT: Tumor Sidedness and the Influence of Adjuvant Chemotherapy Duration on Disease Free Survival (DFS)

Patients with loco-regional right-sided colorectal tumors have a worse overall survival (OS). Here we investigate the difference in disease free survival (DFS) between colorectal patients with right and left sided tumors in the SCOT study.

The SCOT study showed 3-months of oxaliplatin-containing adjuvant chemotherapy (OxFp) is non-inferior to 6-months for patients with stage III and high-risk stage II colorectal cancer. We divided the cohort into patients with left and right sided tumors, and evaluated the effect on DFS and the principle 3 versus 6-months analysis.

6088 patients with Stage III/high risk Stage II colorectal cancers were randomized between 27^th March 2008 and 29^th November 2013 from 244 centers internationally. In February 2017 (3-years FU) information on sidedness was available for 3309 patients (1238 R-sided, 2071 L-sided). Patients with right-sided tumors had a significantly worse DFS (3-year DFS right: 73.3% (se = 1.3%), left: 80.2% (se = 0.9%) HR 1.423 (95% CI 1.237-1.637; P < .0001). Adjusting for T and N-stage reduced the HR to 1.230 (95% CI 1.066-1.420, P = .005). The data did not suggest that sidedness affected the impact of chemotherapy duration on 3-year DFS (R: HR 1.024 [0.831-1.261], L: HR 0.944 [0.783-1.139]). Test for heterogeneity, P = .571. Further sub-set analysis was limited due to cohort size.

This is the first study to show that unselected patients with right-sided tumors had a worse DFS compared to left-sided tumors. Tumor sidedness did not impact upon the 3-months versus 6-months comparison in SCOT.