Benign keratinizing cystic squamous cell tumour in the rat lung

Abstract

Benign keratinizing cystic squamous cell tumours were induced in rat lungs by intratracheal instillation of 15 mg carbon black particles. In this species keratinizing cystic squamous cell tumours are frequently observed after inhalation of intratracheal instillation of particles. Microscopically, the tumours are formed by a sharply demarcated, mostly keratinized squamous epithelium. In the center of the mass there are usually large amounts of keratin and necrotic tumour tissue. Epithelium may be flattened to a thin layer of squamous cells, especially adjacent to pleura or interstitium surrounding major airways and vessels. Growth occurs mainly by peripheral extension into the alveolar spaces. Mitoses are rare. These benign tumours may progress to squamous cell carcinomas, which show destruction of the basement membrane, cellular atypia, disorientation of cells and frequent mitoses