TEE FREQUENCY AND MECHANISM OF LOSS OF HETEROZYGOSITY ON CHROMOSOME 11Q IN BREAST-CANCER

Loss of heterozygosity (LOH, allele loss) occurs frequently on the lon g arm of chromosome 11 in breast cancer, Seventy-one paired tumour/nor mal DNA samples from breast cancer patients under 50 years old were st udied for allele loss at four microsatellite loci on 11q: D11S29 (11q2 3.3), NCAM (11q22-q23), D11S968 (11qtel), and D11S1313 (11qcen), The m aximum frequency of LOH (similar to 35 per cent) was found at the D11S 29 and NCAM loci. This result is consistent with previous studies and the frequency of allele lass is moderate to high compared with the usu al baseline of 0-20 per cent, In most of the cases studied, LOH on chr omosome 11q could be accounted for by one of two mechanisms. Either ch romosomal non-disjunction had occurred, or sequences stretching from t he telomere at least as far as NCAM had undergone deletion or mitotic recombination. These results suggest that a putative tumour suppressor gene is most likely to exist near 11q22-q23, There was a very low fre quency of microsatellite instability in the tumours, An association wa s found between lack of progesterone receptor (PgR) expression and LOH at NCAM, suggesting that deletion of sequences on 11q may prevent hig h levels of PgR expression in some cases.