Clonal IgG lambda plasmacytoma with Mott cell differentiation causing marked pleural effusion in a dog

Area of Science:

• Veterinary Oncology
• Canine Pathology
• Neoplastic Disease Research

Background:

• Canine extramedullary plasmacytomas are typically benign and localized.
• Metastatic and aggressive forms are exceptionally rare.
• This case presents a unique clinical manifestation in a dog.

Purpose of the Study:

• To report a rare case of metastatic extramedullary plasmacytoma in a dog.
• To characterize the cytologic and immunohistochemical findings.
• To discuss the implications of this rare presentation.

Main Methods:

• Cytologic examination of pleural fluid.
• Immunohistochemical staining (CD3, CD20, MUM1, IgG, λ light chain).
• B-cell PCR for antigen receptor rearrangement analysis.

Main Results:

• Pleural effusion with atypical plasma cells and Mott cell differentiation.
• Confirmed clonal IgG lambda extramedullary plasmacytoma.
• Likely metastatic from a non-cutaneous primary site.

Conclusions:

• Metastatic extramedullary plasmacytoma with serous cavity effusion is a novel finding in dogs.
• This presentation carries a grave prognosis, similar to human cases.
• Further research into canine plasma cell neoplasia is warranted.