Rectal Carcinoma With a Sarcomatoid Component: A Case Report With Detailed Immunohistochemistry, Molecular Analysis, and Literature Review.

Introduction. Carcinoma with sarcomatoid components is a highly malignant tumor exhibiting both epithelial and stromal malignant differentiation. Its tumorigenesis is associated with epithelial-mesenchymal transition (EMT), and phenotypic changes from carcinoma to sarcoma are associated with TP53 mutations. Case presentation. A 73-year-old female with bloody stool was diagnosed with rectal adenocarcinoma. She underwent trans-anal mucosal resection. Histopathologically, the tumor cells showed 2 morphologically distinct populations. One was composed of well-formed to fused glands or cribriform glands and was considered a moderately differentiated adenocarcinoma. The other consisted of pleomorphic discohesive atypical tumor cells with spindle and/or giant cell features, which was considered a sarcomatous tumor. Immunohistochemistry analysis showed that E-cadherin expression changed from positive to negative in the sarcomatous component. On the other hand, ZEB1 and SLUG were positive. Finally, she was diagnosed with carcinoma with a sarcomatoid component. We performed a mutation analysis by next genome sequencing and found KRAS and TP53 mutations in both carcinomatous and sarcomatous components. Conclusions. Immunohistochemistry and mutation analyses revealed tumorigenesis of rectal carcinoma with sarcomatoid components correlated with EMT and TP53 mutations.