Mucinous component assessed by magnetic resonance imaging in primary rectal cancer tissue before chemoradiotherapy and tumor response.

768Background: Mucinous carcinoma has been reported to have a lower survival rate, a poorer histologic response to preoperative chemoradiotherapy (CRT) than non-mucinous differentiated adenocarcinoma. Mucinous carcinoma was difficult to diagnose on biopsy because mucinous components are mainly located inside the tumor. We therefore compared MRI findings before and after CRT with histologic findings of resected specimens to investigate the predictive factor of response to CRT. Methods: The study group comprised 205 patients with locally advanced rectal cancer (LARC) who received CRT (40 to 45 Gy) from January 2006 through December 2014. T2-weighted fast-spin echo MRI was used to show the area ratio of mucin lakes (ML) to the maximum cut surface of the primary tissue. The presence or absence of ML and the area ratio of ML on the maximum cut surface were evaluated. Results: The histologic type on preoperative biopsy was well-differentiated or moderately differentiated adenocarcinomas in 202 patients (98.5%),...