EXPRESSION OF C-MYC IN PROGENITOR CELLS OF THE BRONCHOPULMONARY EPITHELIUM AND IN A LARGE NUMBER OF NONSMALL CELL LUNG CANCERS

We performed in situ hybridization for c-myc, N-myc, and L-myc mRNA ex pression using S-35-labeled cRNA probes on frozen sections of 19 pairs of non-small cell lung cancers (NSCLC) and the surrounding non-neopla stic lung tissue. In non-neoplastic lung, c-myc expression was stronge st in bronchial epithelium basal cells and hyperplastic alveolar type II pneumocytes, which are potential progenitor cells for bronchopulmon ary epithelium and their tumors. In contrast, N-myc and L-myc mRNAs we re not detected in non-neoplastic lung. In studies of freshly resected primary tumors, expression of c-myc was detected in 11 of 19 NSCLC (w ith the highest levels in squamous cell carcinomas), two of which also expressed L-myc, while N-myc expression was never detected. Levels of c-myc expression in tumors were significantly higher than in non-neop lastic lung samples. We conclude that: (1) c-myc expression in non-neo plastic lung tissues is highest in bronchial basal cells and hyperplas tic type II cells, and (2) in NSCLC, overexpression of the myc-proto-o ncogene is common.