Mammary carcinoma in a geriatric alpaca

Abstract

An 18-year-old intact, non-lactating, female alpaca presented to the Iowa State University Lloyd Veterinary Medical Center Food Animal and Camelid Hospital for assessment of an inguinal mass noted 2 days prior to shearing. The alpaca was historically multiparous, with her last cria born approximately 1 year prior. On physical exam an 18-centimeter, ulcerated, non-painful mass which produced a thick, white, purulent material and significant crusting was noted in the inguinal region; no normal mammary tissue was appreciated. Clinical differentials were mammary abscess or mammary tumor, the latter of which has not been reported in alpacas. Due to age, cost of therapy and poor prognosis for complete recovery, the owners elected for humane euthanasia and necropsy without further antemortem diagnostic workup. On gross necropsy, the mass was determined to be heterogenous, multilobulated, necrotic and ulcerated with viscous tan to white exudate (Figure 1). Additional findings included multifocal to coalescing pleural nodules and moderate, diffuse lymphadenomegaly of the right inguinal lymph node and mammary lymph node, both of which lacked corticomedullary distinction. On histopathology, a unencapusulated, multilobulated, poorly demarcated, infiltrative neoplasm was diagnosed which completely effaced and replaced normal mammary tissue. Neoplastic cells were epithelial in origin and arranged in nests, islands and tubuloacinar structures, the latter of which contained eosinophilic secretory material (Figure 2). The neoplasm is composed of large polygonal cells arranged in nests, lobules and well differentiated tubules. Neoplastic polygonal cells have distinct cellular borders and abundant hyalinized eosinophilic cytoplasm. Nuclear morphology is characterized by one round hypochromic nucleus per cell, 1–2 nucleoli per nucleus and fine chromatin stippling. There is moderate to marked anisocytosis and anisokaryosis observed throughout the mass. The mitotic index is 5–6 mitotic figures per high power field (0.237 mm2). Multifocal areas of necrosis, inflammation and lymphatic invasion were present throughout with scant areas of normal mammary tissue. The right inguinal lymph node demonstrated regional metastasis but no histopathological evidence of distant metastasis including to the lungs was detected. Here, we report a case of mammary carcinoma in an alpaca. Final diagnosis could not be distinguished between simple tubular carcinoma or mammary ductal carcinoma due to the anaplastic nature of the neoplasm. Previously reported neoplasms in alpacas include fibroma, fibropapilloma, lymphoma, interstitial cell tumor, primitive stromal cell tumor, pancreatic adenocarcinoma, and carcinoma of bronchoalveolar, ocular and of undifferentiated origin.1, 2 Mammary carcinoma of ductal origin has previously been reported in a llama but that case was associated with significant distant metastasis.3 This is the first report of a mammary carcinoma in an alpaca, and it should be considered a differential in future diagnostic investigations of mammary masses. While metastasis to loco-regional lymph nodes was present, distant metastasis was not and may not be the primary concern in future alpacas with mammary neoplasms.