RESUMO
BACKGROUND: The selection of patients for genetic testing to rule out Lynch syndrome is currently based on fulfilment of at least one of the revised Bethesda criteria followed by mismatch repair (MMR) status analysis. A study was undertaken to compare the present approach with universal MMR study-based strategies to detect Lynch syndrome in a large series of patients with colorectal cancer (CRC). METHODS: 2093 patients with CRC from the EPICOLON I and II cohorts were included. Immunohistochemistry for MMR proteins and/or microsatellite instability (MSI) analysis was performed in tumour tissue. Germline MLH1 and MSH2 mutation analysis was performed in patients whose tumours showed loss of MLH1 or MSH2 staining, respectively. MSH6 genetic testing was done in patients whose tumours showed lack of MSH6 expression or a combined lack of MSH2 and MSH6 expression but did not have MSH2 mutations. PMS2 genetic testing was performed in patients showing isolated loss of PMS2 expression. In patients with MSI tumours and normal or not available MMR protein expression, all four MMR genes were studied. RESULTS: A total of 180 patients (8.6%) showed loss of expression of some of the MMR proteins and/or MSI. Four hundred and eighty-six patients (23.2%) met some of the revised Bethesda criteria. Of the 14 (0.7%) patients who had a MMR gene mutation, 12 fulfilled at least one of the revised Bethesda criteria and two (14.3%) did not. CONCLUSIONS: Routine molecular screening of patients with CRC for Lynch syndrome using immunohistochemistry or MSI has better sensitivity for detecting mutation carriers than the Bethesda guidelines.
Assuntos
Neoplasias Colorretais Hereditárias sem Polipose/diagnóstico , Neoplasias Colorretais/diagnóstico , Proteínas Adaptadoras de Transdução de Sinal/genética , Adulto , Idoso , Idoso de 80 Anos ou mais , Neoplasias Colorretais/genética , Neoplasias Colorretais/patologia , Neoplasias Colorretais Hereditárias sem Polipose/genética , Neoplasias Colorretais Hereditárias sem Polipose/patologia , Metilação de DNA , Reparo de Erro de Pareamento de DNA/genética , Feminino , Triagem de Portadores Genéticos/métodos , Testes Genéticos/métodos , Mutação em Linhagem Germinativa/genética , Humanos , Imuno-Histoquímica/métodos , Masculino , Instabilidade de Microssatélites , Pessoa de Meia-Idade , Proteína 1 Homóloga a MutL , Proteína 2 Homóloga a MutS/genética , Proteínas Nucleares/genética , Guias de Prática Clínica como AssuntoRESUMO
Inactivation of MLH1 due to promoter hypermethylation strongly suggests a sporadic origin, providing exclusion criteria for Lynch syndrome. The aim of this study is to compare the utility of methylation analysis of MLH1 and BRAF V600E mutations for the selection of patients with MLH1 negative colorectal cancer for genetic testing. MLH1 methylation status was evaluated by MethyLight and methylation-specific MLPA (MS-MLPA) in tumor DNA from 73 colorectal cancer patients with loss of MLH1 protein expression. These tumors were analyzed for BRAF V600E mutations, and genetic testing for germline MLH1 mutations was performed in all corresponding patients. Ten patients had germline mutations in MLH1 and none of their tumors showed significant MLH1 methylation or BRAF V600E mutation. MLH1 genetic testing excluded patients by MethyLight in 47 patients (64%), by MS-MLPA in 49 (67%), and BRAF V600E mutation in only 25 patients (34%) (chi(2) P = 0.00001). Specificity was 75% for MethyLight, 78% for MS-MLPA and 40% for BRAF V600E mutation. The use of MethyLight or MS-MLPA instead of BRAF mutation resulted in a cost reduction of 41% and 45%, respectively, per every MLH1 mutation detected. Taken together, methylation analysis of MLH1 shows better performance characteristics than BRAF V600E mutation in the selection of patients for genetic testing of MLH1, especially when using MS-MLPA.
