Classification of cystic keratinizing squamous lesions of the rat lung: report of a workshop.

An international workshop of toxicologic pathologists reviewed cystic keratinizing squamous lesions of the rat lung. These lesions develop in response to the chronic inhalation of diverse particulate materials. Controversy exists over the biological significance of these changes and their relevance to humans. For the first time, in one place, a group of pathologists analyzed slides from all available studies. The workshop reached a consensus as to classification of these unique pulmonary tissue responses and offers diagnostic criteria for application. Although additional research is needed, this working classification scheme should serve as a practical interim approach for pathologists and regulatory agencies.