Functional analysis of genetic variants in putative low penetrate breast cancer genes

Paper I & II: CDH1 germline mutations predispose individuals to diffuse gastric cancer, but its role in breast cancer is less clear. Somatic CDH1 mutations were reported to be frequent in lobular tumours (ILC), but they have not been found in ductal carcinomas (IDC). To define the role of CDH1 in breast cancer, we used denaturing high performance liquid chromatography to screen a series of breast cancer samples for mutations. Somatic mutations were detected in 4 of 83 IDC (5%) and 3 of 25 ILC (12%). No germline mutation was found in 19 familial breast cancer patients that showed loss of heterozygosity (LOH) at 16q24, in 12 cases from 10 families with breast, gastric and colon cancer and in 13 familial lobular breast tumours. Another somatic mutation was detected in one of the familial breast cancer patient with both ductal and lobular foci. Putative breast cancer risk conferred by the promoter polymorphism -161C-A of CDH1 or 1774G-A (Ala592Thr) was also analyzed in case-control studies. No significant difference in allelic frequency was found between the breast cancer patients and controls for either polymorphism. A novel promoter polymorphism was identified at position -152 with a similar frequency of the rare C allele in both breast cancer patients and controls. Transient transfection assay using constructs containing -16IC/-152C or -161A/-152T showed only a slight decrease of the transcription activity as compared to the wild type constructs carrying -161C/152T. We conclude that CDH1 is not a prominent lowpenetrance gene in breast cancer, but CDH1 mutations contribute to the progression of both lobular and ductal tumours. Paper III: BACH1, a gene located in 17q22 and encoding a protein directly interacting with BRCA1, was suggested to be a candidate gene for breast cancer susceptibility. Using PCR-SSCP, we screened for germline BACH] mutations with 29 breast cancer families linked to 17q22 and additional 95 familial breast cancer cases, which were all without det