title: High-level microsatellite instability in appendiceal carcinomas.
abstract: High-level microsatellite instability (MSI-high) is found in approximately 15% of all colorectal adenocarcinomas (CRCs) and in at least 20% of right-sided cancers. It is most commonly due to somatic hypermethylation of the MLH1 gene promoter region, with familial cases (Lynch syndrome) representing only 2% to 3% of CRCs overall. In contrast to CRC, MSI-high in appendiceal adenocarcinomas is rare. Only 4 MSI-high appendiceal carcinomas and 1 MSI-high appendiceal serrated adenoma have been previously reported, and the prevalence of MSI in the appendix is unknown. We identified 108 appendiceal carcinomas from MD Anderson Cancer Center in which MSI status had been assessed by immunohistochemistry for the DNA mismatch-repair proteins MLH1, MSH2, MSH6, and PMS2 (n=83), polymerase chain reaction (n=7), or both (n=18). Three cases (2.8%) were MSI-high, and 1 was MSI-low. The 3 MSI-high cases included: (1) a poorly differentiated nonmucinous adenocarcinoma with loss of MLH1/PMS2 expression, lack of MLH1 promoter methylation, and lack of BRAF gene mutation, but no detected germline mutation in MLH1 from a 39-year-old man; (2) an undifferentiated carcinoma with loss of MSH2/MSH6, but no detected germline mutation in MSH2 or TACSTD1, from a 59-year-old woman; and (3) a moderately differentiated mucinous adenocarcinoma arising in a villous adenoma with loss of MSH2/MSH6 expression, in a 38-year-old man with a strong family history of CRC who declined germline testing. When the overall group of appendiceal carcinomas was classified according to histologic features and precursor lesions, the frequencies of MSI-high were: 3 of 108 (2.8%) invasive carcinomas, 3 of 96 (3.1%) invasive carcinomas that did not arise from a background of goblet cell carcinoid tumors, and 0 of 12 (0%) signet ring and mucinous carcinomas arising in goblet cell carcinoid tumors. These findings, in conjunction with the previously reported MSI-high appendiceal carcinomas, highlight the low prevalence of MSI in the appendix as compared with the right colon and suggest that MLH1 promoter methylation is not a mechanism for MSI in this location.
authors: Department of Pathology, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA. mwtaggar@mdanderson.org
authors: Melissa W
authors: MW
authors: Taggart
authors: John
authors: J
authors: Galbincea
authors: Paul F
authors: PF
authors: Mansfield
authors: Keith F
authors: KF
authors: Fournier
authors: Richard E
authors: RE
authors: Royal
authors: Michael J
authors: MJ
authors: Overman
authors: Asif
authors: A
authors: Rashid
authors: Susan C
authors: SC
authors: Abraham
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000032:analysis / Q000235:genetics; D000251:Adenosine Triphosphatases / Q000032:analysis / Q000235:genetics; D000293:Adolescent; D000328:Adult; D000368:Aged; D001063:Appendiceal Neoplasms / Q000737:chemistry / Q000453:epidemiology / Q000235:genetics* / Q000473:pathology; D014408:Biomarkers, Tumor / Q000032:analysis / Q000235:genetics; D002277:Carcinoma / Q000737:chemistry / Q000453:epidemiology / Q000235:genetics* / Q000473:pathology; D019175:DNA Methylation; D004252:DNA Mutational Analysis; D045643:DNA Repair Enzymes / Q000032:analysis / Q000235:genetics; D004268:DNA-Binding Proteins / Q000032:analysis / Q000235:genetics; D005260:Female; D020022:Genetic Predisposition to Disease; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D053842:Microsatellite Instability; D008875:Middle Aged; D000070976:Mismatch Repair Endonuclease PMS2; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein / Q000032:analysis / Q000235:genetics; D009687:Nuclear Proteins / Q000032:analysis / Q000235:genetics; D010641:Phenotype; D016133:Polymerase Chain Reaction; D015995:Prevalence; D011401:Promoter Regions, Genetic; D013781:Texas / Q000453:epidemiology; D055815:Young Adult
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D014408:Biomarkers, Tumor; D004268:DNA-Binding Proteins; C094443:G-T mismatch-binding protein; C501486:MLH1 protein, human; D009687:Nuclear 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
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