Case Report: Modified pulse-dose melphalan therapy for canine colorectal extramedullary plasmacytoma with suspected hepatic dissemination following surgical excision.

A senior male neutered Maltese dog was diagnosed with a solitary rectal extramedullary plasmacytoma that was completely excised with clean margins. 5 months later, multifocal hepatic plasma cell tumors were identified without evidence of multiple myeloma. Systemic chemotherapy was initiated using a pulse-dose melphalan protocol combined with prednisone. Due to recurrent dose-limiting myelosuppression, the treatment protocol was progressively modified by shortening the duration of melphalan administration within a fixed treatment cycle. The modified protocol was associated with clinical improvement, progressive ultrasonographic regression of hepatic lesions, and prolonged disease control, with survival exceeding 19 months following diagnosis of hepatic involvement. Recent reports suggest that some extramedullary plasmacytomas may possess greater metastatic potential than previously recognized. Although limited to a single case, this report describes a practical individualized pulse-dose melphalan adjustment strategy that may serve as a clinical reference for management of biologically aggressive or disseminated extramedullary plasmacytomas in dogs.