GENERAL CONSIDERATIONS

General Considerations

•plasma cell tumors can be single (i.e., solitary or extramedullary plasmacytoma) or diffuse (i.e., multiple myeloma)

•plasma cell tumors arise from a monoclonal (occasionally biclonal) B-lymphocyte cell lineage

•solitary masses of monoclonal plasma cell tumors can originate in either soft tissue or bone:

•soft tissue plasmacytoma = extramedullary plasmacytoma

•bone plasmacytoma = solitary plasmacytoma

•cutaneous, oral, and tracheal extramedullary plasmacytomas are benign

•non-cutaneous extramedullary plasmacytoma have a more aggressive behaviour with gastrointestinal plasmacytoma frequently metastasizing to regional lymph nodes

•however, rectal plasmacytomas have a good prognosis with low metastatic rate

•metastatic extramedullary plasmacytomas do not have a monoclonal gammopathy

•solitary plasmacytoma will often progress to multiple myeloma and may be a precursor to multiple myeloma

•solitary plasmacytoma have a better prognosis in humans, but 50% will still develop multiple myeloma despite appropriate treatment

•5 subclassifications: mature to polymorphous-blastic, but no prognostic significance

Diagnosis

•definitive diagnosis of solitary plasmacytoma requires biopsy proven plasmacytoma in a single site, with:

•normal bone marrow biopsy

•normal serum and urine electrophoresis

•absence of other skeletal lesions

•normal serum or ionized calcium concentrations

•absence of anemia

•normal renal function

CUTANEOUS PLASMACYTOMA

General Considerations

•mean age 9-10 years

•no sex predilection

•breed predisposition: German Shepherd Dog

•sites: trunk, limb, head (especially pinnae), and oral cavity (i.e., tongue and gingiva)

Diagnosis

•pleomorphic round cells with immunoreactivity to canine IgG and vimentin

•systemic involvement rare with only 1 case reported with hypercalcemia and hypergammaglobulinemia

Treatment

•surgery or radiation therapy

•surgery, radiation therapy, or chemotherapy (i.e., melphalan and prednisone) for recurrent tumors

Prognosis

•prognosis is excellent with:

•1.2% develop systemic multiple myeloma

•3.8% local tumor recurrence rate with majority of recurrences due to incomplete resection

•1.8% develop metastasis to other cutaneous sites