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.