Lynch syndrome (LS) is a genetic predisposition leading to colorectal and non-colorectal tumors such as endometrial, upper urinary tract, small intestine, ovarian, gastric, biliary duct cancers and glioblastoma. Though not classically associated with LS, growing literature suggests that sarcomas might develop in patients with LS. This systematic review of literature identified 44 studies (N = 95) of LS patients who developed sarcomas. It seems that most sarcomas developed in patients with a germline mutation of MSH2 (57 %) exhibit a dMMR (81 %) or MSI (77 %) phenotype, as in other LS-tumors. Although undifferentiated pleomorphic sarcoma (UPS), leiomyosarcoma, and liposarcoma remain the most represented histologic subtype, a higher proportion of rhabdomyosarcoma (10 %, especially pleomorphic rhabdomyosarcoma) is reported. Further studies are required to better characterize this sub-population.

Inherited mutations of the DNA Mismatch repair genes MLH1, MSH2, MSH6 and PMS2 can result in two hereditary tumor syndromes: the adult-onset autosomal dominant Lynch syndrome, previously referred to as Hereditary Non-Polyposis Colorectal Cancer (HNPCC) and the childhood-onset autosomal recessive Constitutional Mismatch Repair Deficiency syndrome. Both conditions are important to recognize clinically as their identification has direct consequences for clinical management and allows targeted preventive actions in mutation carriers. Lynch syndrome is one of the more common adult-onset hereditary tumor syndromes, with thousands of patients reported to date. Its tumor spectrum is well established and includes colorectal cancer, endometrial cancer and a range of other cancer types. However, surveillance for cancers other than colorectal cancer is still of uncertain value. Prophylactic surgery, especially for the uterus and its adnexa is an option in female mutation carriers. Chemoprevention of colorectal cancer with aspirin is actively being investigated in this syndrome and shows promising results. In contrast, the Constitutional Mismatch Repair Deficiency syndrome is rare, features a wide spectrum of childhood onset cancers, many of which are brain tumors with high mortality rates. Future studies are very much needed to improve the care for patients with this severe disorder.

Many mismatch repair (MMR) gene disease-causing mutations identified in cancer patients result in aberrant messenger RNA (mRNA) splicing. However, mRNA assay interpretation can be complicated by the existence of naturally occurring alternative mRNA transcripts, most of which have not been formally described or fully characterized. Here, we provide a comprehensive catalogue of all MMR transcripts described to date, and a review of MMR nucleotide variants associated with an apparent upregulation of alternatively spliced transcripts. This work sets reference starting points for designing and interpreting MMR RNA analyses. Our database and literature searches retrieved 30 MLH1, 22 MSH2, 4 MSH6 and 9 PMS2 alternative transcripts, many predicted to introduce premature termination codons. Furthermore, we collected information on 66 MLH1, 24 MSH2 and 6 PMS2 nucleotide variants reported to be associated with altered expression of at least one of these alternative transcripts, and in many instances reported as splicing mutations. This review shows that there are many alternatively spliced MMR transcripts, which have potential to confound interpretation of splicing assays. These findings highlight the need to perform RNA analysis of patients systematically in parallel with control individuals, and call for the implementation of quantitative assessment of transcript levels for informed interpretation of mRNA assays.

Muir-Torre syndrome represents a rare autosomal dominant familial cancer predisposition disorder defined by the occurrence of cutaneous sebaceous tumors and an internal malignancy, most commonly gastrointestinal carcinoma. Most examples of hereditary non-polyposis cancer syndrome (Lynch syndrome), including the Muir-Torre syndrome, are associated with microsatellite instability (MSI) and germline mutations in mismatch repair genes-most commonly MLH1 or MSH2. We present a 58-year-old man with Muir-Torre syndrome and a large retroperitoneal mass (14.3 cm in greatest dimension) encompassing the left adrenal gland. Sections showed a cellular malignant tumor composed of spindle cells with a high mitotic index and lacking morphologic evidence of adipocytic differentiation. It was weakly reactive for smooth muscle actin (SMA) and negative for desmin, CD117, CD31, CD34, S100 protein and pan-cytokeratin. Further immunohistochemical analysis revealed intact expression of MLH1 but loss of MSH2 in tumor nuclei. Compared to non-neoplastic tissue, the tumor showed MSI in five of seven dinucleotide markers. Fluorescence in situ hybridization (FISH) failed to reveal 12q15 amplification, effectively excluding dedifferentiated liposarcoma as a diagnostic consideration. This is a rare case of a patient with Muir-Torre syndrome who developed a related high-grade undifferentiated pleomorphic sarcoma as the associated internal malignancy.