Abstract 863: Clinical significance of mucinous production in rectal cancer after preoperative chemoradiotherapy

Abstract

Abstract Background: Mucinous adenocarcinoma (MA) is a relatively rare histological subtype of colorectal cancer, in which more than 50% of the tumor is occupied by extracellular mucin. MA has been reported to be associated with poor response to neoadjuvant chemoradiotherapy (CRT), but the prognostic significance still remains to be evaluated. Here, we aimed to analyze the prognostic significance of mucin production in the response of rectal cancer to neoadjuvant CRT. Methods: The medical records of 141 consecutive patients receiving rectal resection after neoadjuvant CRT for the treatment of rectal cancer at our institution, in the period between October 2003 and December 2012, were retrospectively reviewed. For the histological evaluation, Hematoxylin-Eosin (HE) and Periodic Acid Schiff/Alcian Blue (PAS/AB) stainings were used. Mucin production was evaluated according to the proportion of the tumor area occupied by extracellular mucin, and cases were sorted, according to the mucin occupancy rate, into three groups, namely, low (0 - 5%), medium (5 - 25%) and high (>25%). Results: The number of patients in the low, medium and high mucin rate groups was 89 (63.1%), 28 (19.9%) and 24 (17.0%), respectively. Only advanced tumor stage out of histological features had a significant correlation with the high mucin rate group. Compared to the low mucin rate group, patients in the high group had a worse prognosis in disease free survival, and also a worse prognosis in distant recurrence free survival, compared to the medium group, while no significant difference was observed among the three groups in overall and local recurrence-free survivals. Multivariate analysis showed that the high mucin rate group had an independent association with shorter disease-free survival, and those advanced stage tumors (T3 and T4) with a high mucin rate had an independent association with shorter distant recurrence-free survival. Conclusion: Mucinous production in rectal cancer may be associated with resistance to neoadjuvant CRT. Thus, careful histological analysis for the presence of extracellular mucin should be indicated for rectal patients receiving neoadjuvant CRT, and those cases with high mucin rate (> 25% mucinous component) should be closely followed-up. Citation Format: Kensuke Kaneko. Clinical significance of mucinous production in rectal cancer after preoperative chemoradiotherapy. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 863. doi:10.1158/1538-7445.AM2014-863