ANALYSIS OF THE FHIT GENE AND FRA3B REGION IN SPORADIC BREAST-CANCER,PRENEOPLASTIC LESIONS, AND FAMILIAL BREAST-CANCER PROBANDS

The FHIT gene, which spans the FRA3B fragile site at chromosome 3p14.2 is a candidate tumor suppressor gene in breast and other cancers. We investigated FHIT and FRA3B for loss of heterozygosity (LOH); homozygo us deletions; abnormal transcripts; and acquired/germ-line point mutat ions in breast cancer cell lines (n = 32), breast epithelial and strom al cell cultures (n = 18), microdissected invasive (n = 16) and ductal in situ carcinomas (n = 6), and their accompanying normal and abnorma l epithelial foci (n = 14). LOH at 3p14.2, especially at FHIT intragen ic marker D3S1300, was found in 6 of 16 microdissected invasive tumors and 3 of 6 ductal in situ carcinomas. In accompanying preneoplastic f oci, LOH occurred in two of eight intraductal hyperplasias but not in histologically normal ductal epithelium (n = 6). Three of 32 (9%) brea st cancer cell lines demonstrated homozygous deletions of FHIT exon 4 (two cases) and exon 5 (one case), which correlated with exon 4-delete d transcripts and loss of the cDNA transcript containing the coding ex ons 5-9, respectively. Normal mammary cultures and 31 or 32 tumor cell lines (97%) expressed wild-type coding transcripts as well as a minor exon 5-deleted message. Single-strand conformation polymorphism analy sis of the coding exons in the 32 tumor and 18 normal breast cell line s and their sequencing revealed four silent polymorphisms and a germ-l ine histidine triad point mutation (651 G-->T) in a tumor arising in a 70-year-old woman. This mutation was also present in one of her two t hus far unaffected daughters. Analysis of additional DNAs from 280 pro bands of high-risk breast cancer families for other FHIT exon 8 mutati ons detected an intronic point mutation 13 bases upstream of exon 8. T hus, we have demonstrated relatively early abnormalities of the FHIT/F RA3B region in breast cancer and discovered two rare FHIT germ-line mu tations. The expression of a transcript containing the coding exons in nearly all cell lines, including those with germ-line mutations, sugg ests the possibility that another gene in the FRA3B region may be invo lved in the pathogenesis of breast cancer.