Multiple Myeloma and Plasmacytomas
Background
Multiple myelomas arise from mature B-cells which usually secrete immunoglobins that are also known as M proteins. There are about 15,000 cases per year in the United States. Multiple myelomas constitute 90% of plasma cell tumors while solitary plasmacytomas constitute 10%.
The incidence in blacks is 2:1 over whites but there is no difference between male and female incidence. The disease is most commonly diagnosed in the 5th - 6th decade.
Ionizing radiation exposure has been linked to Multiple myeloma, particularly with Japanese atomic bomb survivors. There are no apparent strong genetic or environmental patterns other than ionizing radiation exposure associated with multiple myeloma. There may be a modest increased risk of multiple myeloma with radiation exposure. The latency time is twenty plus years. In addition the chemical alachlor, a common pesticide has also been associated with the development of multiple myeloma.
Solitary Plasmacytoma
Solitary plasmacytomas are commonly found in two forms:
- Solitary bone plasmacytomas
- Extramedullary plasmacytomas
Solitary bone plasmacytomas progress to multiple myeloma in 50% - 80% of all patients at 10 years. Unlike solitary bone plasmacytomas, extramedullary solitary plasmacytomas progress to multiple myeloma in only 10% - 40%.
The most common site of solitary extramedullary plasmacytoma are the nasal cavity and paranasal sinuses. Most solitary extramedullary plasmacytomas are non-secretary. Most solitary bone plasmacytomas are secretary. Solitary extramedullary plasmacytomas have lymph node involvement in 30% - 40% of the cases. Solitary bone plasmacytomas rarely have lymph node involvement.
Treatment
Solitary Plasmacytoma
The recommended treatment for solitary plasmacytoma is radiation. Generally doses in excess of 45 Gy have been recommended to the involved field for solitary bone plasmacytomas. Doses used in solitary plasmacytomas are, by definition localized disease and therefore are considered potentially curatable lesions and curative techniques are used. Whereas lower doses of 20 Gy - 30 Gy are used for palliation in multiple myeloma, dose escalation is used in solitary plasmacytomas to total doses of > 45 Gy. Complete eradication of tumor can occur at higher doses.
Ports
Radiation fields should, wherever toxicity permits, some authors recommend the fields encompass the entire medullary cavity of the solitary bone plasmacytoma with a 2 cm - 3 cm margin. Other authors recommend encompassing solitary lesions with a generous margin. In spinal lesions treat the involved vertebral body and 2 vertebral bodies above and below the lesion..
For extraosseous solitary plasmacytomas, the recommended treatment fields are the extraosseous solitary plasmacytoma plus the primary draining lymph nodes.