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
