title: Microsatellite instability is a predictive factor of the tumor response to irinotecan in patients with advanced colorectal cancer.
abstract: The aim of our study was to assess the relationship between colorectal tumor responsiveness to irinotecan and microsatellite instability (MSI), a feature of colorectal tumors with DNA mismatch repair defect. Seventy-two patients with metastatic colorectal cancer were included in our retrospective study. A complete response to irinotecan was observed in 1 patient and a partial response in 10 patients, whereas 61 patients did not respond to this treatment. We analyzed the protein expression of hMLH1, hMSH2, and BAX by immunohistochemistry, determined the MSI phenotype, and looked for mutations in the coding repeats located in the transforming growth factor beta-RII, BAX, hMSH3, and hMSH6 genes. All 44 tumors analyzed expressed detectable levels of hMLH1; 1 tumor lacked hMSH2 staining, whereas 4 tumors showed a marked decrease in BAX expression. A better response to irinotecan was observed in the patients whose tumors have lost BAX expression (P < 0.001). Among the 7 tumors that displayed a MSI-H phenotype, 4 responded to irinotecan, whereas only 7 of the 65 MSI-L/ microsatellite stable tumors did (P = 0.009). Seven of the 72 tumors had inactivating mutations in the coding repeats of the target genes. Three tumors displayed a mutation in the poly-A10 tract of the transforming growth factor beta-RII gene, associated with a 1-bp deletion in the poly-A8 tract of hMSH3 in one tumor and with a 1-bp deletion in the poly-G8 tract of BAX in another. Four tumors displayed mutations in the poly-G8 repeat of BAX, whereas 2 mutations in hMSH6 and hMSH3 were characterized. Among the 7 tumors with mutations in these target genes, 5 responded to irinotecan, whereas only 6 of the other 65 tumors did (P < 0.001), indicating that MSI-driven inactivation of target genes modifies tumor chemosensitivity. Our observations allowed us to define the first useful predictive criteria for irinotecan response in patients with colorectal cancer.
authors.affiliation: Department of Medicine, Institut Gustave Roussy, Centre National de la Recherche Scientifique Unité Mixte de Recherche 1598, Villejuif, France.
authors.forename: David
authors.initials: D
authors.lastname: Fallik
authors.forename: Francesco
authors.initials: F
authors.lastname: Borrini
authors.forename: Valérie
authors.initials: V
authors.lastname: Boige
authors.forename: Jérôme
authors.initials: J
authors.lastname: Viguier
authors.forename: Sandrine
authors.initials: S
authors.lastname: Jacob
authors.forename: Catherine
authors.initials: C
authors.lastname: Miquel
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Sabourin
authors.forename: Michel
authors.initials: M
authors.lastname: Ducreux
authors.forename: Françoise
authors.initials: F
authors.lastname: Praz
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000251:Adenosine Triphosphatases / Q000096:biosynthesis / Q000235:genetics; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D020137:Base Pair Mismatch / Q000235:genetics; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000494:pharmacology*; D002352:Carrier Proteins; D015179:Colorectal Neoplasms / Q000188:drug therapy* / Q000235:genetics* / Q000378:metabolism; D004260:DNA Repair / Q000235:genetics; D045643:DNA Repair Enzymes; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics; D005091:Exons; D005260:Female; D017353:Gene Deletion; D042822:Genomic Instability; D006801:Humans; D000077146:Irinotecan; D008297:Male; D008875:Middle Aged; D000070976:Mismatch Repair Endonuclease PMS2; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics; D009687:Nuclear Proteins; D011237:Predictive Value of Tests; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000235:genetics; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000972:Antineoplastic Agents, Phytogenic; C494826:BAX protein, human; 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; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D000077146:Irinotecan; 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; D002166:Camptothecin