Colorectal Carcinoma in a Young Male Diagnosed as Lynch Syndrome with a Rare PMS2 Pathogenic Germline Variant: A Case Report

Colorectal cancers in young people can be due to inherited mutations in 5-10% of cases, among which Lynch syndrome is the most common. Lynch syndrome is defined as a genetic susceptibility to various types of cancer, with non polyposis colorectal cancer being one of the more common types. A man in his 20s presented with abdominal pain and haematochezia. Upon investigation, the transverse colon showed well-differentiated adenocarcinoma, accompanied by multiple tubulovillous adenomatous polyps of the sigmoid colon with high-grade dysplasia. He underwent surgery followed by chemotherapy, resulting in clinical improvement, resolution of symptoms and a decrease in tumour size and metastasis. Results of genomic testing identified a pathogenic variant located in intron 12 of the PMS2 gene (postmeiotic segregation increased 2), confirming Lynch syndrome. This syndrome, characterised by the PMS2 variant, is extremely rare compared to mutations in other DNA mismatch repair genes such as MLH1, MSH2, MSH6, and EPCAM. Lynch syndrome is thought to account for 2-3% of colorectal cancer cases worldwide and 10-15% of cases in India. The diagnosis of Lynch syndrome is complex and often necessitates a multifaceted approach that includes a thorough evaluation of the patient’s clinical history, clinical evaluation, laboratory testing, and histopathological reporting of biopsy specimens, followed by genetic counselling and genetic testing. His final diagnosis was colorectal cancer with adenomatous polyposis and Lynch syndrome associated with the PMS2 variant.