0-23. High levels of loss of heterozygosity at the ATM and FHIT genes in low grade breast cancers

Abstract

s of the 5th Nottingham International Breast Cancer Conference 231 in the thickness of the skin flap measurement at surgery between patients with positive biopsies, median 8 mm (5-10) and those with negative biopsies, median 7 mm (4-20). Complete removal of all breast tissue cannot be guaranteed by mastectomy and the feasibility of prophylaxis for breast cancer by mastectomy must be questioned. O-23. High levels of loss of heterozygosity at the ATM and FHIT genes in low grade breast cancers Man S Ellis IO, Blarney RW, Brook JD I City Hospital, Nottingham Tumour suppressor genes are commonly identified by loss of heteroaygosity (LOH) studies. We have utilized a sensitive, robust PCR-based assay to measure loss of heterozygosity in archival paraffin-wax embedded breast cancer specimens. 63 pairs of low grade primary sporadic breast cancers were screened for loss of heterozygosity on 11 chromosomal arms, using microsatellite DNA markers. High LOH was identified with selected markers on four chromosomal arms: D3S1300 on 3p (44.4%). DllS923 on llq (38.2%), D3Sl55 on 13q (42.1%). Dl6S402 on 16q (41.2%). This suggests the presence of tumour suppressor genes at these loci, the loss of which is important in cancer development. Candidate genes in these regions include the recently identified fragile histidine triad gene (FHIT) at 3p, which is frequently mutated in lung cancer, the ataxia telangiectasia gene (ATM) at llq and the retinoblastoma (Rbl) and BRCA2 gene at 13q. More detailed typing of chromosome 1 lq identified two distinct common regions of deletion: one coinciding with the ATM gene at 11q22-23 and a second previously unidentified region proximal to ATM at I lql3.5-14. Whilst the ATM gene has been implicated in breast cancer risk, the second region has not. The role of the ATM gene in breast cancer was investigated by looking at 19 of the patients who had showed loss of heterozygosity within the ATM gene and a further 23 patients who had a strong family history of the disease: contracting breast cancer at an early age and having an affected first degree relative. PCR-single-strand conformation polymorphism analysis (PCRSSCP) was used to scan all 65 exons of this 150 kb gene. A total of 21 band shifts were identified in exons throughout the gene. A further scan of 98-100 normal chromosomes revealed that 5 band shifts were unique among the breast cancer patients and the remaining 16 probably polymorphisms. The nature of these band shifts are currently being investigated. Identification of a mutation in the ATM gene would help explain the increased risk of breast cancer in ATM heterorygotes. O-24. Loss of heterozygosity in premenopausal bilateral breast cancer Kollias J, Man S, Ellis IO, Blarney RW, Brook JD City Hospital, Nottingham Women who develop bilateral breast cancer at a young age appear likely to harbour germline mutations in breast canceisusceptibility genes. The aim of this study was to test for concordant genetic changes in left and right cancers of young women (age < 50) with bilateral breast cancer that may suggest an inherited breast cancer predisposition. Microsatellite markers were used to test for loss of heterozygosity (LOH) in left and right tumours for 3 1 women with premenopausal bilateral breast cancer. Markers adjacent to or within candidate genes on 17~ (~53). 17q (BRCAl), 13q (BRCAZ), llq (Ataxia Telangiectasia-AT) and 3p (FHIT) were chosen. The results for Loss of Heteroaygosity are shown in the table. Microsatellite location l7P (P53) 17q (BRCA I ) 13q (BRCA2) I Iq (AT) 3p (FHIT) control LOH for all Cases with informative concordant LOH in cases (%) both cancers