MSH2-Mutated Lynch Syndrome With 9 Synchronous Colon and Rectum Adenocarcinomas: An Extremely Rare Case Report.

Synchronous colorectal carcinoma is having more than 1 primary carcinoma detected in a single patient at the same time or within 6 months of tumor diagnosis. Metachronous colorectal carcinoma is the presence of more than 1 primary carcinoma detected consecutively in a single person after a set time interval. Patients with Lynch syndrome and Muir-Torre syndrome (a subset of Lynch syndrome) inherit a germline mutation in 1 of the mismatch repair (MMR) genes. Patients with synchronous colorectal carcinoma have a higher proportion of MMR-mutated cancers than patients with solitary colorectal carcinoma. Most studies in the literature indicate that patients with synchronous colorectal cancers typically have only 2 carcinomas. However, there have been reports of a single patient having up to 6 synchronous carcinomas in the large intestine. This report discusses a patient with 9 simultaneous colorectal cancers at the initial diagnosis, along with a history of bladder cancer, sebaceous adenoma, and duodenal adenoma, associated with a germline mutS homolog 2 (MSH2) mutation. Additionally, the report explores various aspects of having synchronous colorectal cancers. More studies are needed to clarify the clinicopathologic and molecular landscape of these rare tumors and identify the best management and treatment strategies for these patients.