LAUSR

798Background: Mucinous carcinoma (MC) has been defined as carcinoma with > 50% of tumor volume showing mucin pool (MP). The incidence of MC had been reported to be 4 to 12% of colorectal cancer and to be less effective for chemotherapy and CRT. The incidence of MC was 3 to 8% in rectal cancer treated with surgery alone and 13 to 24% in patients treated with CRT. These findings suggest that MP may be induced by CRT in some patients. We therefore compared the degree of MP in MRI findings before CRT, after CRT and in resected specimens. Methods: The study group comprised 205 patients with rectal cancer who received CRT (40 to 45 Gy) from 2006 through 2014. MPs on MRI were evaluated using T2-weighted fast-spin echo images, and the MP area ratios on maximum cross-section of the primary tumor were calculated. An MP area ratio of 0% was designated as class 0, 1 to 9% as class I, 10 to 29% as class II, 30 to 50% as class III, and 50% or higher as class IV. Results: On MRI before CRT, the MP area ratio was class ...