Recto-Sigmoid Synchronous Malignant Tumor with Lack of MLH1 and PMS2 Expression: Case Report and Literature Review

Background: Synchronous colorectal cancers are defined by the presence of at least two cancers (primary self-standing tumors) in the same time, in the same patient. In these conditions, the tumor with the maximum diameter has nomenclatures such as “primitive”, or “index”. The preoperative diagnosis of synchronous tumors is very important, as it can turn into metachronous tumors, which require a new surgical intervention.

Case report: In the following, we report a case of a 54 year-old patient without any related oncological family history but with important cardiovascular comorbidities, who has been operated for stenotic synchronous cancer of the recto-sigmoid junction and middle rectum. During the initial work-up, no liver or peritoneal metastases were noted on the CT scan. The surgical intervention opted for was a recto-sigmoid laparoscopic with subtotal mesorectal excision followed by a termino-terminal mechanical stapled colorectal anastomosis. The histopathological examination showed both lesions to be moderately differentiated (G2) adenocarcinomas, with subserosal invasion in 2 of the 12 detected lymph nodes. Immunohistochemistry further revealed microsatellite instability, with MLH1 and PMS2 mutation.

Conclusion: The literature review highlights certain particular aspects regarding the clinical, surgical and morphological management of such cases compared to cases with single tumor. The peculiarity of this case was laposcopic resection of the colon segment, and the microsatellite instability of the specimen, assessed by ancillary studies. Early preoperative diagnosis of synchronous tumors allows the selection of appropriate therapeutic management, depending on their location at the level of the affected colonic segments.