Abstract
The Shope rabbit papilloma, a skin growth caused by a virus, 1 has been shown to possess the characters whereby tumors are recognized. 2 When given opportunity, as on implantation within the host, the growth frequently looks and behaves like a malignant neoplasm. The present report is concerned with instances in which skin papillomas caused by the virus have spontaneously become carcinomatous. The change has been noted in 5 of 10 domestic rabbits with growths existing 4 to 8 months.
During the early weeks of its development after virus inoculation the papilloma enlarges laterally, but later it is restricted by scar tissue and builds outwards only. At first it overlies the skin appendages, but these disappear after a time and it becomes bedded somewhat more deeply. The malignant change may first attract attention when a fissure exuding serosanguineous fluid opens in the midst of the papilloma; but more often there occurs a generalized, fleshy, discoid thickening of the base of the growth, which gradually raises the jagged, dry, papillomatous tissue some millimeters above the skin surface, and also bulges downwards. Soon the animal gnaws at this portion of the growth, opening in the one case a depressed ulceration with firm, gristly walls, and in the other laying bare a high, fungoid mass. On biopsy a squamous cell carcinoma is found, or an invasive, papillomatous, epithelial tumor, or most frequently, the 2 intermixed, with every gradation between them. The growth may for some weeks remain circumscribed and fungating, or it may rapidly extend under the skin, involving it and the muscle and becoming fixed upon the deep tissues. Some cancers less than 2 months old are already 5 cm. across and 2–3 cm. deep. As a rule they become infected with pus-producing organisms and the health of the host suffers, though most of our rabbits are still alive. Metastasis to a regional lymph-node (confirmed by section) has occurred once. Transplantation to the leg muscle of the host has resulted in a secondary, highly invasive, squamous cell carcinoma.
Get full access to this article
View all access options for this article.