Purpose To investigate the clinicopathological and molecular features of colorectal micropapillary carcinoma(MPC),and to provide evidence for the diagnosis and individu-al treatment of colorectal MPC.Methods The clinicopathologi-cal and molecular data of 461 patients with colorectal cancer were collected retrospectively,including 56 cases of colorectal MPC and 405 cases of colorectal adenocarcinoma not otherwise specified(NOS).The expression of 4 mismatch repair proteins(MLH1,PMS2,MSH2,MSH6)and p53 protein was detected by immunohistochemistry.The hot spot mutations of KRAS,NRAS,PIK3CA and BRAF genes were detected by ARMS-PCR,to analyze the difference of clinicopathological and molec-ular features between colorectal MPC and adenocarcinoma NOS.Results The vessel invasion rate and lymph node metastasis rate of colorectal MPC were significantly higher than those of ad-enocarcinoma NOS(42.9％vs 23.0％,P=0.001;67.9％vs 46.2％,P=0.002).The incidence of mismatch repair defi-ciency in colorectal MPC was significantly lower than that in ade-nocarcinoma NOS(3.6％vs 13.8％,P=0.030).The hot spot mutation rate in exon 2,3 and 4 of KRAS gene in colorectal MPC was significantly higher than that in adenocarcinoma NOS(58.9％vs 42.2％,P=0.018),especially in KRAS G13D(17.9％vs 8.1％,P=0.019).The proportion of colorectal MPC components was not associated with clinicopathological and molecular features.There were no significant differences in clin-icopathological and molecular features between colorectal MPC and adenocarcinoma NOS with high-grade tumor budding.Con-clusion The clinicopathologic and molecular features of color-ectal MPC are different from those of adenocarcinoma NOS,and the diagnosis of this subtype may provide help for the formulation of treatment plan and the evaluation of prognosis.
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