The significance of mucin pools following neoadjuvant chemoradiotherapy for locally advanced rectal cancer

Abstract Background Neoadjuvant chemo‐radiotherapy is utilized for locally advanced rectal cancer to optimize local control. A subset of patients form mucin pools following radiotherapy but the association between mucin pools and pathological and oncological outcomes following curative proctectomy for rectal cancer remains unknown. Objective The aim of this study was to determine the significance of mucin pool formation after neoadjuvant chemoradiotherapy for rectal cancer. Methods This is a retrospective analysis of a prospectively maintained rectal cancer database. Patients who underwent curative proctectomy for rectal cancer following long course chemoradiotherapy between January 2007 and December 2016 were eligible for inclusion. Results A total of 297 patients were eligible for inclusion; of these 36 (12.1%) had mucin pools on final histopathology. Tumors with mucin pools were less likely to be ypT3/T4 (25.0 vs 51.0%, P = 0.003), were more likely to have a good response (83.3 vs 53.6%, P < 0.001) and more likely to have a pathologic complete response (41.7 vs 19.2%, P = 0.006) to radiotherapy. The presence of mucin pools was associated with less distant recurrence ( P < 0.05) and improved overall survival ( P = 0.02). Conclusions The presence of mucin pools following neoadjuvant chemoradiotherapy for rectal cancer represents a surrogate marker of response to treatment and downstaging and is associated with improved survival.