RESUMO
PURPOSE: The relationships between mismatch repair (MMR) protein expression, microsatellite instability (MSI), family history, and germline MMR gene mutation status have not been studied on a population basis. METHODS: We studied 131 unselected patients with colorectal cancer diagnosed younger than age 45 years. For the 105 available tumors, MLH1, MSH2, MSH6, and PMS2 protein expression using immunohistochemistry (IHC) and MSI were measured. Germline DNA was screened for hMLH1, hMSH2, hMSH6, and hPMS2 mutations for the following patients: all from families fulfilling the Amsterdam Criteria for hereditary nonpolyposis colorectal cancer (HNPCC); all with tumors that were high MSI, low MSI, or that lacked expression of any MMR protein; and a random sample of 23 with MS-stable tumors expressing all MMR proteins. RESULTS: Germline mutations were found in 18 patients (nine hMLH1, four hMSH2, four hMSH6, and one hPMS2); all tumors exhibited loss of MMR protein expression, all but one were high MSI or low MSI, and nine were from a family fulfilling Amsterdam Criteria. Sensitivities of IHC testing, MSI (high or low), and Amsterdam Criteria for MMR gene mutation were 100%, 94%, and 50%, respectively. Corresponding positive predictive values were 69%, 50%, and 75%. CONCLUSIONS: Tumor IHC analysis of four MMR proteins and MSI testing provide a highly sensitive strategy for identifying MMR gene mutation-carrying, early-onset colorectal cancer patients, half of whom would have been missed using Amsterdam Criteria alone. Tumor-based approaches for triaging early-onset colorectal cancer patients for MMR gene mutation testing, irrespective of family history, appear to be an efficient screening strategy for HNPCC.
Assuntos
Pareamento Incorreto de Bases , Neoplasias Colorretais Hereditárias sem Polipose/epidemiologia , Neoplasias Colorretais Hereditárias sem Polipose/genética , Predisposição Genética para Doença/epidemiologia , Mutação em Linhagem Germinativa , Proteínas Adaptadoras de Transdução de Sinal , Adenosina Trifosfatases/genética , Adulto , Idade de Início , Biomarcadores Tumorais/genética , Biomarcadores Tumorais/metabolismo , Proteínas de Transporte , Estudos de Coortes , Neoplasias Colorretais/diagnóstico , Neoplasias Colorretais/epidemiologia , Neoplasias Colorretais/genética , Neoplasias Colorretais Hereditárias sem Polipose/diagnóstico , Análise Mutacional de DNA , Reparo do DNA , Enzimas Reparadoras do DNA/genética , Proteínas de Ligação a DNA/genética , Feminino , Testes Genéticos , Humanos , Masculino , Repetições de Microssatélites , Pessoa de Meia-Idade , Endonuclease PMS2 de Reparo de Erro de Pareamento , Proteína 1 Homóloga a MutL , Proteínas de Neoplasias/genética , Proteínas Nucleares/genética , Prevalência , Medição de Risco , Proteínas de Saccharomyces cerevisiae/genética , Sensibilidade e EspecificidadeRESUMO
The aim of our study was to examine the role of genetic factors on early-onset colorectal cancer after excluding the impact of germline mutations in the two major mismatch repair genes. A total of 131 incident probands, under 45 years at diagnosis of a first primary colorectal cancer selected from the Victorian Cancer Registry, and their first-and second-degree relatives, were interviewed. Germline DNA from all 12 probands with a family history meeting the modified Amsterdam Criteria for Hereditary Non-Polyposis Colorectal Cancer (HNPCC) and a random sample of 31 of the remaining probands was screened for mutations in hMSH2 and hMLH1 via manual sequencing. Germline mutations were identified in 6 of the 131 probands (5%), all from the "HNPCC" families. Of the remaining 125 probands, 51 (41%) reported at least one first-or second-degree relative with colorectal cancer with an excess of colorectal cancer in first-degree relatives (SMR = 2.7, 95% CI = 1.7-4.1, p < 0.001). The lifetime risk to age 70 for first-degree relatives was 8.0% (5.0-12.8%), compared to the Victorian population risk of 3.2% (p = 0.01). The best fitting major gene model was a recessively-inherited risk of 98% to age 70 (95% CI = 24-100%) carried by 0.17% of the population and would explain 15% of all colorectal cancer in cases with a diagnosis before age 45. Early-onset colorectal cancer is strongly familial even after excluding families found to be segregating a mutation in either of the 2 major mismatch repair genes. There is evidence for a role of yet to be identified genes associated with a high recessively-inherited risk of colorectal cancer.