Biology and treatment of multiple myeloma.
The uniformly fatal plasma cell malignancy, multiple myeloma (MM), currently represents 10-15% of hematologic neoplasms in the USA and has been steadily increasing in incidence for several decades. Therapeutic alternatives have lagged significantly behind insights into the biology and pathogenesis of this entity. Traditionally felt to be a neoplasm of fully differentiated plasma cells, evidence has been mounting that the self renewing population consist of cells derived from a much earlier compartment; perhaps prior to B-cell lineage commitment or even at the level of an earlier 'stem cell'. Bcl-2 protein overexpression has been almost uniformly seen in both clinical myeloma specimens as well as in myeloma cell lines. The failure to consistently identify the t(14;18) translocation, normally found in follicular lymphomas and characteristically associated with overexpression of bcl-2, implies a unique mechanism in MM. A number of cytokines, including TNF alpha, IL-1 and IL-6 have been found to play a central role not only in the biology of the malignant clone but also in the bony and other systemic manifestations of this disease. Since both IL-6 and bcl-2 protein have been shown to prevent programmed cell death, this may be the unifying event in MM. Standard therapy for MM has been an alkylating agent and corticosteroid. Combination chemotherapy provides more prompt palliation but no clear survival advantage. In advanced stages, adriamycin may offer some survival advantage. High dose chemotherapy with or without stem cell support offers a potentially curative therapeutic approach. New interventions directed at the complex cytokine networks pertinent to the pathogenesis of MM are an exciting new area of investigation. Identification of new prognostic parameters as well as new active agents remains the central theme in clinical myeloma research.