Morphological comparison between benign keratinizing cystic squamous cell tumours of the lung and squamous lesions of the skin in rats.

Approximately 700 cases of keratinizing cystic squamous lung lesions in rats were investigated by light microscopy in order to clarify the nomenclature and classification of these lesions. The structure of benign keratinizing cystic squamous cell tumours of the lung was compared to that of cystic squamous lesions in the skin of rats, with consideration of data from the literature. We conclude that the reviewed keratinizing cystic squamous cell lesions of the lung are true neoplasms and that the growth pattern of these cystic lesions is inconsistent with that of a simple cyst. In the development of squamous lung cancer, a continuum of proliferation from exaggerated metaplasia through benign cystic tumours to invasive squamous cell carcinomas can be observed.