Cystic keratinizing squamous cell carcinomas in the lung of Syrian hamsters induced by a coal oven flue exhaust mixed with pyrolized tar pitch in combination with benzo(a)pyrene

Induced pulmonary squamous cell carcinomas with pronounced formation of keratin lamellae in male Syrian hamsters (strain Cpb-ShGa51, TNO, Zeist, The Netherlands) are described. Male and female Syrian hamsters inhaled an aerosol containing a mixture of pyrolized tar pitch and coal oven flue exhaust (PCE) for up to 22 months. In addition, serveral hamsters were treated intertracheally with 0.1 mlenzo(a)pyrene (30 x 100 µg B(a)P/animal or 30 x 300 µg B(a)P/animal). Ten Syrian hamsters (10 of 48) of the group which received PCE and 30 x 300 µg B(a)P developed squamous cell tumours. Most of these tumours contained large central masses of keratin and were classified microscopically as cystic keratinizing squamous cell carcinomas. Two of the neoplasms showed only limited features of malignicancy. Their histological structure was characterized by a large mass of lamellated keratin which contained a small amount of cellular debris and was surrounded by a thin rim of stratified squamous epit hel ium. They were sharply demarcated from the surrounding pulmonary parenchyma and had some projections into the central keratin mass of epithelial cells. In significant portions of the wall, the cell had variations in size, shape, orientation, nuclear/cytoplasmic ratio and increased mitotic figures which were restricted to the basal layers. In the tumours with more pronounced malignant features, the central keratin was enveloped by epithelial cells that frequently revealed papillary or solid projections into the keratin. The tumours were not well demarcated. Focally, stratifcation of the epithelium was lost and the cells were irregularly arranged. Pleomorphism of the cells was marked and mitotic figures were frequent.