Syndrome of early onset colon cancers, hematologic malignancies & features of neurofibromatosis in HNPCC families with homozygous mismatch repair gene mutations

Hereditary nonpolyposis colon cancer (HNPCC) is the most common hereditary colon cancer syndrome. It is characterized by multiple colon as well as extracolonic cancers such as endometrial, ovarian and urinary tract cancers. In addition, it is well known that some cases of HNPCC can present with unique tumor spectrums such as sebaceous tumors, which is often referred to as the 'Muir-Torre' syndrome. In recent years there have been a few reports of families presenting with early onset of colon tumors along with cafe-au-lait spots and/or hematologic malignancies often associated with homozygous mutations involving one of the mismatch repair genes. In this article we have performed a comprehensive review of the entire medical literature to identify all cases with similar presentations reported in the literature and have summarized the clinical features and genetic test results of the same. The available data clearly highlight such presentations as a distinct clinical entity characterized by early onset of gastrointestinal tumors, hematologic malignancies as well as features of neurofibromatosis (easily remembered by the acronym 'CoLoN'; Colon tumors or/and Leukemia/Lymphoma or/and Neurofibromatosis features). Furthermore, there has also been some evidence that the neurofibromatosis type-1 gene is a mutational target of the mismatch repair deficiency that is seen in families with HNPCC, and that mlh1 deficiency can accelerate the development of leukemia in neurofibromatosis (Nf1) heterozygous mice. Recognition of this syndrome has significant importance in terms of earlier detection of cancers, cancer screening recommendations as well as genetic counseling offered to such families.