Does stage III rectal mucinous adenocarcinoma benefit from neoadjuvant chemoradiation?

This study aimed to compare clinical outcomes of patients with clinical stage III mucinous rectal adenocarcinoma (M) and non-mucinous rectal adenocarcinoma (NM) and evaluate the effectiveness of neoadjuvant chemoradiation. It was hypothesized that patients with M would fare worse with neoadjuvant chemoradiation than those with NM and that patients with M and NM not receiving chemoradiation would have similar outcomes. Moreover, it was hypothesized that patients with M would have similar outcomes regardless of chemoradiation.

This study compares eligible patients distributed in three cohorts: (cohort 1) M versus NM, including only patients treated with neoadjuvant chemoradiation; (cohort 2) M versus NM, including only patients treated without neoadjuvant chemoradiation; and (cohort 3) only M patients treated with versus without neoadjuvant chemoradiation.

We identified 515 patients with an average age of 58.8 (SD 12.4) years, and 30% were female. Fifty-seven (11.1%) patients had M and 458 (88.9%) had NM. Neoadjuvant chemoradiation was administered to 382 (74%) patients, of whom 41 (10.7%) were M and 341 (89.3%) NM.

In cohort 1, patients with M had advanced pathological staging (stage 3: M 68% vs. NM 42%; p < 0.001), worse pathological differentiation (poor: M, 37% vs. NM, 11%; p = 0.001), more involved lymph nodes (M 0 [0;7] vs. NM 0 [0;1]; p < 0.001) and a higher rate of local recurrence (M 22% vs. 3%; p < 0.001). Patients with M demonstrated worse 7-year cancer-specific (p = 0.007) and overall survival (p = 0.01). There were no significant differences in cohort 2 and 3.

Patients with clinical stage III mucinous adenocarcinomas may not benefit as much from standard neoadjuvant chemoradiation as their non-mucinous counterparts do.