Constitutional Mismatch Repair Deficiency (CMMRD) Syndrome: A Case Report of a Patient With Multiple Metachronous Malignancies.

Defective repair of DNA when heterozygous leads to Lynch syndrome (LS) which is inherited in an autosomal dominant fashion. When homozygous, defective repair of DNA leads to constitutional mismatch repair deficiency syndrome (CMMRD), inherited in an autosomal recessive fashion with a predisposition to develop a pattern of childhood malignancies including hematological and solid cancers. We report such a case of a 21-year-old male who developed anaplastic astrocytoma, Burkitt lymphoma, osteochondroma, and colon cancer successively. Each cancer was treated successfully except for colon cancer which developed liver metastasis after the initial treatment with curative intent. However, the patient has been treated for liver metastasis with curative intent and is currently on follow-up. This case report highlights the importance of maintaining a low threshold for investigating CMMRD and other potential cancer predisposition syndromes when a patient presents with multiple cancers in the early years of their life.