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 cytogenetic abnormalities found in human breast carcinoma. We examined genetic alterations on chromosome 1q in 124 human breast tumors, using restriction fragment length polymorphism markers mapping to the long arm (13 markers) and short arm (4 markers). Imbalance of heterozygosity at 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 loss 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 gain and/or loss of the entire long arm of chromosome 1. Detailed alteration mapping of the other 25 tumors showing partial alterations of chromosome 1q 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 suppressor genes are present on chromosome 1q and are associated with breast tumorigenesis.