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.
Causes 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.
Terminology There can be some ambiguity when using the
"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.
Diagnosis 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.
Treatment Surgical excision is the treatment of choice
for plasmacytomas and generally results in a favorable prognosis.
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