Dark epithelial cells in preneoplastic lesions of the human respiratory tract

Dark epithelial cells, previously identified in preneoplastic lesions of rat tracheae induced with chemical carcinogens, were observed in similar lesions in human airways and investigated using plastic-embedded material from the lungs of 21 autopsy cases. The lesion types and the percentage of dark cells in their basal layers were as follows: squamous metaplasia without atypia = 13 +/- 3%, squamous metaplasia with slight atypia = 13 +/- 3%, squamous metaplasia with moderate atypia = 26 +/- 5%, squamous metaplasia with severe atypia = 27 +/- 4%, and carcinoma in situ = 34 +/- 11%. Notwithstanding a technical complication caused by differences in fixation and embedding procedures, it was possible to detect an increase in the number of dark cells in human preneoplastic lesions that was directly proportional to the degree of atypia. This increase points to the importance of these cells in neoplastic development and indicates that, regardless of their nature, the number of dark cells can be used as an indicator of the degree of atypia.