Anaplastic cutaneous plasmacytoma in a dog

Abstract Extramedullary cutaneous plasmacytoma is an uncommon tumour in dogs and rare in cats, often linked to chronic inflammation or prolonged antigenic stimulation. It typically affects middle‐aged to older dogs, involving the head, trunk, limbs and digits. Although usually benign, anaplastic forms exhibit high malignancy, pleomorphism, hyperchromatic nuclei and high mitotic activity. This report describes a 10‐year‐old, female French bulldog with ulcerated nodules on the fifth digit of the left hindlimb and the cervical dorsum, accompanied by intense pruritus. Laboratory tests were unremarkable, and fine‐needle aspiration suggested a round cell neoplasm but was inconclusive. Incisional biopsy showed malignant features without definitive tumour typing. Immunohistochemistry revealed positivity for multiple myeloma oncogene 1, confirming a high‐grade anaplastic plasmacytoma. The patient began chemotherapy, but developed multiple nodules and neurological signs, ultimately resulting in death.