Case of the Week: Sweetie
Two patients, both canines, presented on the same day with similar exam findings. Sweetie, a 10-year-old, F/S Pit Bull was evaluated for a golf-ball sized mass associated with the soft palate. Gem, a 14-year-old, F/S Yorkshire Terrier has recent history of difficulty breathing and was treated for presumptive upper respiratory disease with steroids and antibiotics. Gem did not improve, became dyspneic, and on examination a large, dark colored mass was found in the region of the hard and soft palate interface. FNAs of oral masses submitted.
Sweetie: The cells often appear individually or in small aggregates, and are round to slightly fusiform, features reminiscent of round cell or mesenchymal neoplasms. There is varying amounts of fine green-gray granular pigmentation, with some cells lacking pigment, while others have densely pigmented cytoplasm. Numerous small rod-shaped pigment granules are in the background. In this case, binucleation is often present. Note the anisokaryosis, anisocytosis, and prominent nucleoli.
Gem: The sample is very cellular, with cells closely associated in sheets, a feature that is similar to cohesive epithelial neoplasms rather than the round/mesenchymal appearance of Sweetie’s neoplastic cells. There is a greater amount of pigment both within the cells and in the background. Numerous pigment granules are in the background. In this case, criteria of malignancy include increased mitotic activity and karyomegaly, among others.
Additional information: Melanoma is the most common malignant neoplasm of the oral cavity in dogs. Cytologic evaluation is often used to confirm this type of neoplasia when clinically suspected, but biopsy is recommended to evaluate prognostic indicators, such as mitotic index and degree of invasiveness. Location itself is a prognostic indicator, with oral melanoma typically being malignant with high risk of metastasis. The benign counterpart to malignant melanoma is the cutaneous melanocytoma, however cutaneous melanocytic neoplasms should also be biopsied to confirm expected benign behavior and complete excision.
The cytologic features of these two cases demonstrate the microscopic variation, as well as overlap, observed in this tumor type. Cytologically, malignant melanomas can have features of epithelial, mesenchymal, or round cell tumor types, which could create a diagnostic dilemma since other oral tumors include sarcomas and carcinomas, but instead this often raises suspicion of potential melanocytic origin. Degree of pigmentation varies, with some tumors lacking visible pigment (amelanotic melanoma), while others are densely pigmented.
In both cases, expedited turnaround time for diagnosis allowed direct referral of these patients to oncologists for additional case management and therapeutic planning. This was particularly important for Gem given her clinical sign of dyspnea.
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