+ 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


+ 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