A plasmacytoma (malignant tumour of plasma cells) is a discrete, solitary mass of neoplastic monoclonal plasma cells in either bone marrow or a soft tissue site. Plasmacytoma can arise in any part of the body. Solitary plasmacytomas can be divided into 2 groups according to location: Plasmacytoma of the skeletal system (solitary bone plasmacytoma) and soft tissue plasmacytoma (extra-medullary plasmacytoma). Solitary bone plasmacytoma arises from the plasma cells located in the bone marrow, while soft tissue plasmacytoma is thought to arise from plasma cells located in mucosal surfaces. Both represent a different group of tumors in terms of sex predilection, location, tumour progression, and overall survival rate.
The diagnostic criteria vary but the current accepted criteria using magnetic resonance imaging (MRI), flow cytometry, and polymerase chain reaction (PCR) are as follows:
Single area of bone destruction due to clonal plasma cells
Normal bone marrow without evidence of clonal plasma cell proliferation
Normal findings on skeletal survey and MRI
Absence of anaemia, hypercalcemia, or renal impairment caused by myeloma
Low concentrations of serum or urine monoclonal protein and normal levels of uninvolved immunoglobulins
The treatment of choice for solitary bone plasmacytoma is local radiotherapy which leads to local control and relief of symptoms in almost all patients. The local tumor recurrence rate is less than 10%. Although surgery is not usually advised, it may be required sometimes to reestablish the normal architecture of the spine or other bone affected. This type of tumor has a 10-year disease-free survival rate of 15-46%, and the overall median survival time is 10 years. Most patients progress to multiple myeloma at a rate of 65-84% at 10 years and 65-100% at 15 years.
Radiotherapy is usually the treatment for soft tissue plasmacytoma but if a lesion can be completely resected, surgery provides the same results as radiotherapy. Combined therapy (surgery and radiotherapy) also is an accepted treatment depending on the respectability of the lesion. The rate of progression of soft tissue plasmacytoma to multiple myeloma is lower than in solitary bone plasmacytoma, ranging from 11-30% at 10 years.
Periodic evaluation for progression and development of multiple myeloma is recommended every 6 months for solitary bone plasmacytoma and soft tissue plasmacytoma.