LOSS AND GAIN OF DISTINCT REGIONS OF CHROMOSOME 1Q IN PRIMARY BREAST-CANCER

Alterations of the long arm of chromosome 1 are the most frequent cyto genetic abnormalities found in human breast carcinoma. We examined gen etic alterations on chromosome 1q in 124 human breast tumors, using re striction fragment length polymorphism markers mapping to the long arm (13 markers) and short arm (4 markers). Imbalance of heterozygosity a t one or more loci on the long arm was observed in 80 (65%) of the 124 tumors, Among these 80 tumor DNAs, 38 showed an allele gain, 16 a los s of heterozygosity, and 1 both allele gain and loss of heterozygosity at each locus on the long arm, indicating that 55 tumor DNAs had a ga in and/or loss of the entire long arm of chromosome 1. Detailed altera tion mapping of the other 25 tumors showing partial alterations of chr omosome Iq identified two distinct altered regions: a smallest common deleted region at 1q21-31 and a smallest common overrepresented region at 1q41-q44. The results suggest that both oncogenes and tumor suppre ssor genes are present on chromosome Iq and are associated with breast tumorigenesis.