PROXIMAL 6Q, A REGION SHOWING ALLELE LOSS IN PRIMARY BREAST-CANCER

To define regions of deletion of chromosome 6q in breast cancer, we sc ored 18 (CA)(n) microsatellites for allelic imbalance (AI) in 42 paire d blood/tumour samples. Heterozygosity frequencies of the markers in t he sample population ranged from 31% to 92% (mean 68%). Two regions of the chromosome arm showed Al values greater than the background range of 10-22% (mean 17%) of informative cases that was observed with five markers spanning 6q21-q25.2. Firstly, seven markers gave Al values th at averaged 35% in a region flanked by D6S313 (AI = 10%) at 6q13 and D 6S283 (AI = 17%) at 6q16.3-21. The second region showed marginally inc reased Al at 6q25.2-q27 and included D6S193, previously shown to be cl ose to a tumour-suppressor gene involved in ovarian carcinoma. Since A I of 6q in breast cancer was shown previously to be due predominantly to loss of heterozygosity, our results suggest the presence of at leas t two tumour-suppressor genes on 6q that are involved in breast cancer . The proximal region has not been recognised in breast cancer before and is involved in a higher frequency of tumours than the distal regio n.