title: Defective mismatch repair in the pathogenesis of low-grade appendiceal mucinous neoplasms and adenocarcinomas.
abstract: Defective DNA mismatch repair has been proposed as a second pathway for colonic carcinogenesis, particularly in tumors arising in the right colon. We investigated whether tumors arising in the appendix are associated with defective DNA mismatch repair using immunohistochemistry for mismatch repair enzymes hMLH-1, hMSH-2, hMSH-6, and hPMS-2. These immunoassays have been shown to be highly sensitive and specific for defective DNA mismatch repair in sporadic and familial adenocarcinomas. Sporadic adenocarcinomas with defective DNA mismatch repair essentially always show loss of hMLH-1, while loss of hMSH-2, hMSH-6, or hPMS-2 is almost always due to germline mutation. In all, 35 cases of appendiceal epithelial neoplasms were evaluated, comprising 18 low-grade appendiceal mucinous neoplasms confined to the appendix; eight low-grade appendiceal mucinous neoplasms with extra-appendiceal spread (five peritoneum and ovaries, two peritoneum, one ovaries only); and nine invasive adenocarcinomas (three with metastatic disease). All immunohistochemical slides were reviewed by two pathologists. One (11%) invasive adenocarcinoma showed absent expression of hMSH-2 and hMSH-6, but preserved hMLH-1 and hPMS-2 expression. This case was a 26-year-old female with a history of synovial sarcoma who presented with acute appendicitis and appendiceal perforation (median age for other invasive carcinomas, 62 years; range 38-76 years). The appendiceal tumor was a moderately differentiated, colonic-type adenocarcinoma without significant extracellular mucin or tumor-infiltrating lymphocytes. The remaining invasive carcinomas and low-grade appendiceal mucinous neoplasms demonstrated preserved expression of all mismatch repair enzymes, including the seven cases in which extra-appendiceal tumor was also evaluated. We conclude that defective DNA mismatch repair does not play a role in the pathogenesis of low-grade appendiceal mucinous neoplasms. Defective DNA mismatch was found in 11% of invasive carcinomas, likely due to a germline mutation. These findings suggest that sporadic appendiceal neoplasia rarely arises through the defective DNA mismatch repair (mutator) pathway.
authors.affiliation: James Homer Wright Pathology Laboratories at the Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA. jmisdraji@partners.org
authors.forename: Joseph
authors.initials: J
authors.lastname: Misdraji
authors.forename: Lawrence J
authors.initials: LJ
authors.lastname: Burgart
authors.forename: Gregory Y
authors.initials: GY
authors.lastname: Lauwers
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000230:Adenocarcinoma / Q000378:metabolism / Q000473:pathology*; D002288:Adenocarcinoma, Mucinous / Q000378:metabolism / Q000473:pathology*; D000251:Adenosine Triphosphatases / Q000032:analysis; D001063:Appendiceal Neoplasms / Q000378:metabolism / Q000473:pathology*; D020137:Base Pair Mismatch; D002352:Carrier Proteins; D004260:DNA Repair; D045643:DNA Repair Enzymes / Q000032:analysis; D004268:DNA-Binding Proteins / Q000032:analysis; D006801:Humans; D007150:Immunohistochemistry; D000070976:Mismatch Repair Endonuclease PMS2; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein; D009363:Neoplasm Proteins / Q000032:analysis; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins / Q000032:analysis
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C094443:G-T mismatch-binding protein; C501486:MLH1 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D000251:Adenosine Triphosphatases; C094934:PMS2 protein, human; C497172:MSH2 protein, human; D000070976:Mismatch Repair Endonuclease PMS2; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein; D045643:DNA Repair Enzymes