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Immunohistochemistry (IHC) for mismatch repair (MMR) proteins is recommended in endometrial carcinomas as a screening test for Lynch syndrome, and mismatch repair deficiency (MMRd) is reported in ∼30% of cases. However, few studies have evaluated the rate of MMR loss in uterine carcinosarcomas. A 5-year retrospective database search of uterine carcinosarcomas was performed at 3 academic institutions. The histologic diagnoses, type of carcinoma present, and MMR IHC interpretations were confirmed by a gynecologic pathologist. One hundred three cases of uterine carcinosarcomas with available MMR IHC results were identified. Ninety-nine cases (96%) showed intact expression and 4 cases (4%) showed loss of MLH1/PMS2. All MMRd carcinosarcomas identified in this series had an endometrioid carcinomatous component and wild-type p53 expression. In contrast, the majority of MMR intact carcinosarcomas had a serous morphology and aberrant p53 expression. Three additional cases initially diagnosed as carcinosarcoma also revealed MMRd; however, given the lack of clear mesenchymal differentiation, these cases were reclassified as dedifferentiated endometrial carcinomas and were subsequently excluded from the carcinosarcoma category. No cases of Lynch syndrome were identified among carcinosarcoma patients, as all 4 MMRd cases were due to somatic MLH1 hypermethylation. In summary, we found that the rate of MMRd is markedly lower in uterine carcinosarcoma when compared with endometrial carcinoma. In the setting of MMR loss, a diagnosis of dedifferentiated carcinoma should be considered as almost half of the MMRd tumors which were called carcinosarcomas initially were reclassified as dedifferentiated on review. However, given the interobserver variability in the classification of carcinosarcoma versus dedifferentiated carcinoma a universal screening approach that includes uterine carcinosarcoma is still recommended.
This article was published in the following journal.
Name: The American journal of surgical pathology
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Eukaryotic homolog of the bacterial MutL DNA MISMATCH REPAIR protein. It heterodimerizes with MISMATCH REPAIR ENDONUCLEASE PMS2 to form MutL alpha, which is recruited to DNA mismatch sites by the MUTS DNA MISMATCH-BINDING PROTEIN. Mutations in the human MLH1 gene are associated with COLORECTAL NEOPLASMS, HEREDITARY NONPOLYPOSIS.
A MutL protein and component of the DNA MISMATCH REPAIR system. Its ENDONUCLEASE activity introduces SINGLE-STRAND DNA BREAKS which create entry points for EXO1 exonuclease to remove the strand containing the mismatch. It may also function in DNA DAMAGE signaling.
DNA repair proteins that include the bacterial MutL protein and its eukaryotic homologs. They consist of a conserved N-terminal region with weak ATPase activity, an endonuclease motif, and a C-terminal domain that forms MutL homodimers or heterodimers between MLH1 and the PMS1, MISMATCH REPAIR ENDONUCLEASE PMS2; or MLH3 proteins. These complexes function in DNA repair pathways, primarily DNA MISMATCH REPAIR, where MutL/MLH1 and the MUTS DNA MISMATCH-BINDING PROTEIN are targeted to damaged DNA.
DNA repair proteins that include the bacterial MutS DNA mismatch-binding protein and its eukaryotic homologs that function in DNA MISMATCH REPAIR and recombination of DNA during MEIOSIS. MutS has a conserved mismatch recognition domain characterized by GxFxE, or similar AMINO ACID MOTIFS that also occur in eukaryotic homologs such as MSH1, MSH6, and MSH8. All MutS proteins also contain a highly-conserved ATP-binding domain and most have weak ATPase activity.
A DNA repair pathway involved in correction of errors introduced during DNA replication when an incorrect base, which cannot form hydrogen bonds with the corresponding base in the parent strand, is incorporated into the daughter strand. Excinucleases recognize the BASE PAIR MISMATCH and cause a segment of polynucleotide chain to be excised from the daughter strand, thereby removing the mismatched base. (from Oxford Dictionary of Biochemistry and Molecular Biology, 2001)