CHROMOSOMAL DUPLICATION ACCOMPANIES ALLELIC LOSS IN NONSMALL CELL LUNG-CARCINOMA

Hemizygous deletion in the short (p) arm of chromosome 3 is a common f inding in non-small cell lung carcinoma (NSCLC) and is postulated to b e a crucial early change in lung tumorigenesis, Yet one of the most fr equent nuclear abnormalities in both NSCLC and premalignant bronchial epithelium is increase in chromosomal copy number. Deletion and duplic ation have not been assessed in the same tumor set by both molecular a nd cytogenetic methods to determine whether allelic loss correlates wi th chromosomal duplication in the same tumor cell populations. It is a lso not established what biological mechanisms might lead to allelic d eletion and chromosomal duplication. We have investigated changes in t he copy number of chromosome 3 in touch preparations of 38 NSCLCs (19 adenocarcinomas and 19 squamous cell carcinomas) using dual-target, du al-color fluorescence in situ hybridization (FISH) assays. Chromosome 3 centromere probe was matched with a 3p14.2 probe [intron 4 of the fr agile histidine triad (FHIT) gene] and a 3p21.31. probe (HSemaIV gene) . We then correlated FISH results with results of molecular analyses f or allelic losses at loci in the regions to which the FISH probes mapp ed in. 20 of these cases, Although various combinations of FISH abnorm alities were sometimes detected within the same specimens, individual cases could be classified according to the predominant FISH pattern, u sually with one abnormality present in >60% of tumor cells. Chromosoma l duplication, indicated by the presence of more than two centromeric signals, was the most frequent abnormality observed by FISH and was ac companied by loss of specific sequences on 3p in approximately one-hal f of the specimens in which it was observed. The most frequent abnorma lity observed by molecular analysis was loss of heterozygosity (LOH) i n both of the chromosomal regions tested and was demonstrated in 83% o f eases with chromosomal duplication. We conclude that LOH may occur i n the presence of chromosomal duplication, suggesting that the duplica ted chromosome is homozygous, Our findings imply that LOH occurs befor e chromosomal duplication during lung carcinogenesis.