Presumed primary muscular lymphoma in a dog.

A case of presumed primary muscular lymphoma in an 8-year-old, intact, male Newfoundland dog is reported. The dog was presented for evaluation of an infiltrating ventral cervical mass, respiratory distress, and anorexia of 1-month duration. Fine-needle aspiration of the mass revealed anaplastic large cell lymphoma. Despite chemotherapy, health status declined and the animal was euthanized a few weeks later. At necropsy, the mass infiltrated the cervical muscles and extended ventrally to the left forelimb and cranially to the tongue and laryngeal musculature. Other muscles were infiltrated by the same neoplasm (diaphragm and intercostal, abdominal, and gluteal muscles) indicating a probable multicentric origin. Histological examination confirmed the diagnosis of anaplastic large cell lymphoma, which showed a strong muscular tropism. Immunohistochemical staining revealed neoplastic cell reactivity for cluster of differentiation 3 (CD3) and Ki-67 antigens (70% and 90%, respectively). The neoplastic cells were negative for CD79a. The presumed histological diagnosis in this dog was primary muscular anaplastic large T-cell lymphoma.