LOSS OF HETEROZYGOSITY STUDIES IN TUMORS FROM FAMILIES WITH BREAST-OVARIAN CANCER SYNDROME

A gene (BRCA1) predisposing for familial breast and ovarian cancer has been mapped to chromosome band 17q12-21. Based on the observation tha t ovarian tumors from families with breast and ovarian cancer lose the wild-type allele in the region for the BRCA1 locus, it has been sugge sted that the gene functions as a tumor suppressor gene. We have studi ed chromosomal deletions in the BRCA1 region in seven breast tumors, t hree ovarian tumors, one bladder cancer, and one colon cancer from pat ients in six families with breast-ovarian cancer, in order to test the hypothesis of the tumor suppressor mechanism at this locus. We have f ound a low frequency of loss of heterozygosity at this region, and our results do not support the idea that BRCA1 is a tumor suppressor gene . Alternatively, the disease segregating in these families is linked t o one or more different loci.