Pathogenesis of tumors induced with N-nitrosomethylpiperazine in the olfactory region of the rat nasal cavity.

Tumors in the olfactory region of the nasal cavity of the F344 rat were induced by chronic treatment with N-nitrosomethylpiperazine. The pathogenesis of the neoplasms was studied in a serial sacrifice study by light and electron microscopy. Proliferating basal cells of the olfactory epithelium differentiated into cells with morphologic features of neuroendocrine cells, which then progressed further to become invasive carcinomas. The tumors exhibited areas of neuroendocrine, adenoid, squamous, and neuroblastic morphologies. The variability of morphologic patterns found within the same tumor can be explained by the ability of neuroendocrine cells to differentiate into these different cell types.