RESUMO
Colorectal cancers (CRC) with microsatellite instability (MSI) or mismatch repair-deficiency (dMMR), but without detectable MMR germline mutations are termed Lynch-like syndrome (LLS). We assess the clinicopathologic and molecular characteristics of LLS tumors and the proportion in LLS, which remain poorly investigated in China. We enrolled 404 CRC patients with surgery in our institution from 2014 to 2018. LLS tumors were detected by a molecular stratification based on MMR protein expression, MLH1 methylation and MMR gene mutation. LLS tumors were profiled for germline mutations in 425 cancer-relevant genes. Among 42 MMR-deficient tumors, 7 (16.7%) were attributable to MLH1 methylation and 7 (16.7%) to germline mutations, leaving 28 LLS cases (66.6%). LLS tumors were diagnosed at a mean age of 60.7 years, had an almost equivalent ratio among rectum, left colon and right colon, and had high rates of lymph node metastases (50%, 4/28 N2). Most MMR gene mutations (88.2%, 15/17) in LLS tumors were variants of unknown significance (VUS). Two novel frameshift mutations were detected in ATM and ARID1A, which are emerging as candidate responsible genes for LLS. In this study, 28 (66.6%) MMRd tumors were classified as LLS, which were significantly higher than reports of western countries. LLS tumors were more likely to carry lymph node metastases. However, it's hard to differentiated LLS tumors from LS through family history, tumor location, histological type of tumors, immunohistochemistry (IHC) for MMR proteins and MSI analysis.
RESUMO
BACKGROUND: Colorectal cancer is one of the most common tumors with high mortality in China. Microsatellite instability (MSI) analysis is important for the diagnosis of hereditary non-polyposis colorectal cancer (HNPCC) and for the prediction of 5-FU chemotherapy efficiency of colorectal tumors, especially in terms of therapeutic response and overall survival rates. Among the MSI markers recommended by the NIH/NCI, BAT-25 has been extensively studied for its major role in MSI. BAT-25 presents different polymorphisms in different ethnic populations and studies of its polymorphisms in the Chinese population are still very limited. AIMS: To analyze the frequency of constitutive polymorphic variation at the BAT-25 locus in Chinese from Jiangsu Province and its implication for locus MSI screening. METHODS: The frequency of allelic variation at the BAT-25 locus of cervical cells from 500 healthy women and blood from 16 healthy males was assessed by direct sequencing. Twenty samples were also analyzed by fragment analysis. DNA extracted from blood of 94 patients with gastrointestinal cancer or endometrial cancer was analyzed by fragment analysis. RESULTS: After comparison with the sequencing results, the more frequent allele lengths were 126-127 bp, 128-129 bp, 129-130 bp, respectively consistent with the 24 poly(T) (T24), T25 and T26 alleles. At the BAT-25 locus, 516 healthy individuals had respectively 1.36%, 97.28% and 1.36% of the T24, T25 and T26. Whereas for the 94 cancer patients allelic frequencies were 0.53%, 1.06%, 96.8%, 1.6% for T15, T24, T25 and T26 alleles respectively. Sixteen healthy males had only the T25 allele and heterozygous T15 was only found in 1 male patient with colon cancer. CONCLUSION: We established the relation between fragment length and thymine repeats in BAT-25. The results showed that the BAT-25 locus is quasimonomorphic in Chinese from Jiangsu province. Moreover we showed that variant alleles of BAT-25 were found more likely in blood from cancer patients than in healthy individuals, suggesting the need to perform comparative studies between tumor and blood, or normal tissue, as to obtain a correct MSI identification.