Expression of c-myc in progenitor cells of the bronchopulmonary epithelium and in a large number of non-small cell lung cancers.

We performed in situ hybridization for c-myc, N-myc, and L-myc mRNA expression using 35S-labeled cRNA probes on frozen sections of 19 pairs of non-small cell lung cancers (NSCLC) and the surrounding non-neoplastic lung tissue. In non-neoplastic lung, c-myc expression was strongest in bronchial epithelium basal cells and hyperplastic alveolar type II pneumocytes, which are potential progenitor cells for bronchopulmonary epithelium and their tumors. In contrast, N-myc and L-myc mRNAs were not detected in non-neoplastic lung. In studies of freshly resected primary tumors, expression of c-myc was detected in 11 of 19 NSCLC (with 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-neoplastic lung samples. We conclude that: (1) c-myc expression in non-neoplastic lung tissues is highest in bronchial basal cells and hyperplastic type II cells, and (2) in NSCLC, overexpression of the myc-proto-oncogene is common.