ABSTRACT. Multiple yellowish-white, cauliflower-like mass lesions on the skin of the head and back in a 4-month-old piglet were pathologically examined. These lesions had developed before the weaning period. Histologically, the cutaneous neoplasms were characterized by papillary outgrowth of connective tissue covered by thick epidermis. Hyperplasia of the epidermis was corresponded with proliferation of capillaries, lympho-plasmacytic infiltration, and proliferation of fibroblasts in the dermal stroma. There were no inclusion bodies and significant degeneration in the keratinocytes. Papillomavirus antigen and DNA were not detected in these lesions by immunohistochemistry and polymerase chain reaction, respectively. Accordingly, the fibropapillomatosis of the present case might be hamartomatous rather than infectious.KEY WORDS: dermatopathology, fibropapilloma, hamartoma, pathology, swine.J. Vet. Med. Sci. 73(2): 283-285, 2011 Cutaneous papilloma is rare in pigs, and two patterns of the lesion have been reported: transmissible genital papilloma and congenital fibropapilloma [7,13]. Only two cases of porcine congenital papilloma have been reported, and the involvement of viral infection in the cutaneous lesion has not been confirmed [11,16].In animals and humans, some forms of cutaneous papilloma are caused by papillomavirus (PV). In particular, bovine papilloma virus (BPV) types 1, 2, and 5 induce fibropapilloma of the skin in cattle [4,6]. Congenital papillomas are considered non-infectious lesions that most often occur in horses [5,14,17]. In a previous report on porcine congenital papilloma, the presence of virus was not found on electron microscopy, but there have been no studies using immunohistochemistry or polymerase chain reaction (PCR) to assess for viral involvement [16]. We recently encountered cutaneous papillomatosis in a piglet. In this report, we describe the histopathological features and the results of immunohistochemistry and PCR for PV.A hybrid piglet developed multiple, yellowish-white, cauliflower-like tumors on the skin of the head and back. According to the owner, these lesions had been observed from the suckling period (Fig. 1), and the animal had not shown any other significant clinical abnormalities. The pig was sacrificed at 4 months of age and the liver, intestine, lymph nodes, and 4 tumors were submitted to our laboratory for pathological examinations. The largest tumor among those submitted was approximately 8.0 × 7.0 × 5.0 cm in size and was hard, creamy white, and pedunculated on cut section (Fig. 2).Tissue samples were fixed in 10% neutral-buffered formalin and embedded in paraffin wax. The sections (4 μm) were cut and stained with hematoxylin and eosin (HE). For immunohistochemical examination, a standard peroxidaseantiperoxidase technique was used on the paraffin sections with primary antibodies as rabbit polyclonal anti-bovine papillomavirus (BPV-1) (DakoCytomation, Carpinteria, CA, U.S.A.) and mouse monoclonal anti-proliferating cell nuclear antigen (PCNA) (clone PC10; DAKO...