Colorectal cancer in Lynch syndrome associated with PMS2 and MSH6 mutations.

Background: It is known that colorectal cancers (CRC) are frequently seen and constitute an important part of cancer-related deaths. Lynch syndrome (LS) is responsible for 3-5% of CRCs and develops due to mutations in DNA mismatch repair (MMR) genes. The most important MMR genes are MutL homolog1 (MLH1), mutS homolog 2 (MSH2), mutS homolog 6 (MSH6) and postmeiotic segregation increased 2 (PMS2). PMS2 and MSH6 mutations are very rarely seen in LS.

Case Presentation: We present a case that developed metastatic CRC, which we diagnosed as LS in association with a very rarely seen PMS2 and MSH6 germline mutation. Genetic counseling was recommended for the family, and screening programs were initiated for the family of the patient whose chemotherapy was continued after the diagnosis.

Conclusion: With the increase in daily use of next-generation sequencing (NGS) technology, it is thought that detection rate of both combined mutations and rare mutations will be increased.