Malignant pilomatricoma in a soft‐coated Wheaten Terrier

Abstract

A 3-year-old, castrated male, soft-coated Wheaten Terrier was presented for evaluation of mild lameness, fecal incontinence, lumbosacral pain, and lack of anal tone. Magnetic resonance imaging scan showed a large (8 x 6 x 5 cm) mass invading and expanding the pelvic bones, sacrum, and associated structures. A fine-needle aspirate of the mass contained many neoplastic cells with high nuclear to cytoplasmic ratios and rare spindle and inflammatory cells. The neoplastic cells were 12-16 mum in diameter, round to cuboidal, basaloid in appearance, and arranged both individually and in loosely cohesive clusters with variably distinct cell borders. Given the location, signalment, and cytologic findings, differential interpretations included a primitive embryonal tumor (eg, neuroblastoma or nephroblastoma in an atypical location) or poorly differentiated carcinoma. The owner elected euthanasia due to the poor prognosis. Abnormal gross findings on necropsy included the pelvic mass and multiple firm, pale, pink-tan nodules in the lung, which proved to be metastases. On histologic examination, the mass and nodules were composed of irregular islands, lobules, and nests of basaloid cells, which transitioned abruptly into large lakes of "ghost" cells with areas of ossification and calcification, consistent with a diagnosis of malignant pilomatricoma. This unusual presentation of a pilomatricoma adds to our knowledge of expected cytologic findings for this tumor.

Malignant Pilomatricoma in a Dog

“…Canine malignant pilomatricoma is prone to metastasize to bones (Van Ham et al, 1990;Rodr ıguez et al, 1995;Carroll et al, 2010;Jackson et al, 2010), as was observed in the present case. A number of carcinomas, melanomas and sarcomas metastasize to the liver via the pulmonary and hepatic arteries.…”

“…No reports describe metastasis to the central nervous system and the neurological signs were attributed to invasion of bones (Sells and Conroy, 1976;Johnson et al, 1983;Van Ham et al, 1990;Rodr ıguez et al, 1995;Carroll et al, 2010;Jackson et al, 2010). In the present case, the animal had lameness due to bone lysis caused by metastases to the left and right humerus and L5 to L7 vertebrae.…”

“…In the present case there was a similar number of epithelial and ghost cells, moderate nuclear atypia and few mitotic figures. Other findings described for malignant pilomatricoma in man and dogs, such as foci of transition to inner or outer root sheath and non-specific formation of squamous epithelium, necrosis, lymphatic invasion and contiguity with the epidermis (Johnson et al, 1983;Rodr ıguez et al, 1995;Hardisson et al, 2001;G alvezAranda et al, 2002;Carroll et al, 2010;Jackson et al, 2010), were not present in the primary tumour. It is important to emphasize that even without the presence of accentuated malignant characteristics, the tumour metastasized to several organs.…”

“…Affected dogs usually present with neurological signs and lameness due to bone metastasis (Van Ham et al, 1990;Carroll et al, 2010;Jackson et al, 2010). These tumours are characterized by their locally aggressive behaviour with tendency to recur.…”

Malignant Pilomatricoma in a Young Dog

“…This is the fi rst case of MP in a young dog. Although MP is rarely observed in dogs, the incidence of MP in dogs is on the rise [2,3,[5][6][7][8][9][10][11]. We suggest that the incidence of MP could increase not only in the older dogs, but also in the younger ones.…”