ALLELE-SPECIFIC LOSS IN CHROMOSOME 9P LOCI IN PRENEOPLASTIC LESIONS ACCOMPANYING NON-SMALL-CELL LUNG CANCERS

Background: Carcinogenesis is a multistep process, which may begin as a consequence of chromosomal changes. Deletions in the short arm of ch romosome 9 (9p) have been observed in lung carcinomas. In addition, mo rphologically recognizable preneoplastic lesions, frequently multiple in number, precede onset of invasive carcinomas. Purpose: We tested fo r deletions and loss of heterozygosity (LOH) at 9p loci in preneoplast ic and neoplastic foci in lungs of patients with non-small-cell lung c arcinomas (NSCLCs). Methods: Seven archival, paraffin-embedded, surgic ally resected NSCLC specimens were selected. They were predominantly f rom patients with adenocarcinomas and contained multiple preneoplastic lesions, including hyperplasia, metaplasia, dysplasia, and carcinoma in situ (CIS). Fifty-three histologically identified preneoplastic and malignant lesions present in bronchi, bronchioles, and alveoli were p recisely microdissected from stained tissue sections with a micromanip ulator. Stromal lymphocytes were used to determine constitutional hete rozygosity. The specimens were analyzed for LOH using polymerase chain reaction-based assays for polymorphism in dinucleotide repeats (micro satellite markers) in interferon alfa (IFNA) and D9S171 loci on 9p. Re sults: All seven cases were constitutionally heterozygous for one or b oth microsatellite markers. Five of seven cases had LOH at one or both 9p loci in the invasive primary cancers (doubly informative cases). F our of these five cases also revealed LOH in preneoplastic foci. In th e doubly informative cases, LOH was detected in five (38%) of 13 foci of hyperplasia, four (80%) of five foci of dysplasia, and three (100%) of three CIS lesions. LOH was detected in preneoplastic lesions from all regions of the respiratory tract, including bronchi, bronchioles, and alveoli, and involved five different cell types. The identical all ele was lost from both the preneoplastic lesions and the corresponding tumors (12 of 12 lesions, 17 of 17 comparisons), a phenomenon we have referred to as ''allele-specific mutation.'' Statistical analyses emp loying a cumulative binomial test demonstrated that the probabilities of such findings occurring by chance are 2.4 x 10(-4) and 7.6 x 10(-6) , respectively. From comparisons with the previously published data on other chromosomal abnormalities in the same tissue specimens, it appe ars that LOH at 3p and 9p loci occurred early in the hyperplasia stage , but the ras gene point mutations were relatively late, at the CIS st age. Conclusions: LOH at 9p loci occurs at the earliest stage in the p athogenesis of lung cancer and involves all regions of the respiratory tract. LOH in NSCLC is not random but targets a specific allele in in dividuals. Studying preneoplastic lesions may help identify intermedia te markers for risk assessment and chemoprevention.