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Issue Description
Extramedullary plasmacytomas are tumors of plasma cells that occur outside the bone marrow cavity. The most common location of these neoplasms is the skin or mucous membranes, especially the lip, digits, trunk, ears, and face. Plasmacytomas are not very common tumors in dogs, but it is thought that they may be underrepresented due to misclassification as different tumor types.

They usually occur on older dogs, with a mean age between 9 and 10 years. There appears to be no sex predilection although some studies found that more males than females were affected. While many breeds were represented in these reports, one study found that Cocker Spaniels were more commonly affected.

There can be some ambiguity when using the word:
  • "Plasmacytoma" is sometimes equated with "plasma cell dyscrasia" or "solitary myeloma".
  • It is often used as part of the phrase "solitary plasmacytoma".
  • It is also used as part of the phrase "extramedullary plasmacytoma ". In this context, "extramedullary" means outside of the bone marrow.

  • Symptoms
    Plasmacytomas are usually solitary raised nodules that appear red and sometimes ulcerated, especially neoplasms on the digits. Cutaneous and mucocutaneous plasmacytomas usually lack clinical signs of disease; however, oral and rectal plasmacytomas have been associated with gagging or rectal prolapse, respectively. If signs of generalized illness are present concurrently, the possibility of multiple myeloma should be excluded.

    It is diagnosed by immunoglobulin electrophoresis (or Serum protein electrophoresis) and bone marrow biopsy. Immunoglobulin electrophoresis will show a monoclonal M spike, but bone marrow biopsy will fail to find the classical signs of multiple myeloma. After those two determinations are made, search for the primary site in the soft tissue begins.

    Surgical excision is the treatment of choice for plasmacytomas and generally results in a favorable prognosis.

    Canine (muco)cutaneous plasmacytomas are mostly benign and thus differ from both multiple myelomas and extramedullary plasmacytomas of internal organs, which often metastasise. After surgical excision of (muco)cutaneous plasmacytomas, dogs have remained tumour-free for long periods, although metastasis to lymph nodes has been reported. Whether these metastases originated from primary (muco)cutaneous plasmacytomas or from multiple myeloma remains unclear, because tests were not carried out to exclude the possibility of primary multiple myeloma.

    The relationship between the localisation or cell type of the (muco)cutaneous plasmacytomas and their biological behavior have been investigated to determine the prognosis of these tumours. The clinical outcome of cutaneous plasmacytomas is not influenced by either anatomical site or histological appearance. However, well-differentiated tumours are most often found in the skin of the lip and the ear, whereas the poorly differentiated tumours preferentially affect the skin of the digits. Results from one study suggested less benign behavior for plasmacytomas with the polymorphous-blastic cell type, whereas in another study it was concluded that almost all cases had a good prognosis.

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