Long-Term Survival in a Dog After Adrenalectomy and Splenectomy for Two Different Malignancies with Portal Vein Involvement.

Concurrent occurrence of two independent primary malignancies in a single dog is rare and presents diagnostic and surgical challenges. A 9-year-old neutered male Cocker Spaniel was diagnosed with adrenal pheochromocytoma and splenic diffuse large B-cell lymphoma. Abdominal imaging revealed two distinct masses. Surgical management included adrenalectomy, splenectomy, mesenteric lymphadenectomy, and excision of a small mass adherent to the portal vein adventitia. Histopathology confirmed two separate malignancies, with chromogranin A positivity supporting pheochromocytoma and CD20 positivity confirming B-cell lymphoma. No additional metastatic lesions were identified, and the portal vein-associated mass was considered an isolated lesion closely adherent to the vessel wall, with its exact pathogenesis remaining uncertain. To the authors' knowledge, this represents the first veterinary report describing adrenal pheochromocytoma with portal vein involvement successfully managed by surgical removal. The patient recovered well and remained disease-free for three years without adjuvant therapy. This case emphasizes that, even in technically demanding situations, meticulous surgical planning and comprehensive oncologic assessment can achieve durable remission and inform future approaches to complex veterinary cancers.