A 2-year-old, 4.8 kg, intact male, domestic short-hair was presented to the referring veterinarian for examination of a mass in the left ear canal. It was a barn cat on a small beef farm. The owner had noticed the mass 3 d previously and was concerned because it had begun to bleed. On physical examination, the cat was found to be in good body condition and no other abnormal findings were noted, other than the ear mass. Closer examination revealed a 2- × 2-cm, pedunculated, ulcerated nodule within the external ear canal. Otoscopic examination of the ear revealed no other abnormal findings. The mass was excised and the cat was castrated and subseqently discharged.
Histologically, the exophytic mass extended from a focally ulcerated surface into the underlying deep dermis. It consisted of tightly packed interwoven bundles of spindle-shaped cells with varying amounts of collagenous matrix (Figure 1). The spindle-shaped cells had small to moderate amounts of poorly delineated pale acidophilic cytoplasm. The nuclei were round to oval with vesicular to finely granular chromatin, single to inapparent nucleoli, and moderate anisokaryosis. Mitotic figures were present in occasional random high power fields. Moderate numbers of well-differentiated mast cells and occasional eosinophils were scattered throughout the mass. In nonulcerated areas, there was moderate epidermal hyperplasia with several long thin rete pegs and occasional palisading of the spindle cells at the interface with the rete pegs. The clinical findings and microscopic features of this tumor are characteristic of feline cutaneous fibropapilloma (1,2,3,4). Follow-up information on this case indicated that the mass had returned within a few weeks after surgery. At that point, due to financial considerations, the owners opted for euthanasia.
Over a 4-year period, from January 1998 to December 2001, the diagnostic pathology service at the Atlantic Veterinary College has diagnosed 13 cases of cutaneous fibropapillomas in cats from a case load of approximately 1400 feline surgical biopsies. The gross descriptions provided by the submitting clinicians were of firm, alopecic, and often focally ulcerated skin masses that occurred almost exclusively on the face (especially nose, lip, and pinna) or digits.
From the first descriptions of feline cutaneous fibropapillomas in the 1990s, the morphologic similarity to equine sarcoids was immediately recognized (2,4). Since equine sarcoids have a strong association with papillomaviruses (5), a similar association was investigated in cats. Early investigations proved negative (6); however, a recent report provides strong evidence of an association of feline fibropapillomas with bovine papillomavirus (3). In the study reported, DNA could be amplified by polymerase chain reaction in 17 of 19 feline fibropapillomas, and all 17 of these tumors were positive for a papillomavirus, most similar to bovine papillomavirus type 1.
These tumors are rare, with outdoor rural cats and those with known exposure to cattle having an apparently higher prevalence (1,3). They typically occur as nodular masses, up to 2 cm in diameter, that are often ulcerated and are found most commonly on the head, neck, ventral abdomen, and limbs. Like equine sarcoids, local recurrence of feline cutaneous fibropapillomas is common, but metastasis has not been reported.
The frequency of occurrence of feline cutaneous fibropapilloma is thought to be underestimated for a variety of reasons. These include misdiagnosis, especially as granulation tissue; fibroma; or fibrosarcoma, when the overlying epithelium is lost due to ulceration, or when only small biopsies of the entire mass are submitted for histopathologic examination. Also, because the tumors are generally self-limiting and are thought to affect a rural population of cats, they are not as likely to receive veterinary attention. It is hoped that an increased awareness of feline cutaneous fibropapilloma will lead to a more accurate estimate of its true prevalence and that experimental investigations will determine the role of bovine papillomavirus in their development.