Multiple Myeloma and Other Plasma Cell Dyscrasias
Plasma cell dyscrasias are a heterogeneous group of disorders characterized by the accumulation of monoclonal plasma cells or plasmacytoid B lymphocytes and are frequently associated with the overproduction of a monoclonal immunoglobulin product, the M pr
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Plasma cell dyscrasias are a heterogeneous group of disorders characterized by the accumulation of monoclonal plasma cells or plasmacytoid B lymphocytes and are frequently associated with the overproduction of a monoclonal immunoglobulin product, the M protein. Although there are several plasma cell dyscrasias, multiple myeloma will be the focus of this chapter.
23.1 Epidemiology and Risk Factors 23.1.1 Incidence and Distribution The average age-adjusted annual incidence for myeloma in whites is 4.3 (of 100,000) men and 3.0 in women [1]. In blacks, the incidence is higher: 9.6 for men and 6.7 for women. With age, the incidence increases with fewer than 2% of cases being younger than 40 years at diagnosis [2]. In the United States, the median age of onset is 68 years for men and 70 for women [3]. From the late 1940s to the late 1970s, the incidence and mortality rates for myeloma had risen, with net increases of 145% [4]. This trend, however, may reflect prior underdiagnosis and not a true increase.
23.1.2 Risk Factors and Etiology Genetic and environmental factors have been implicated in the pathogenesis of myeloma. With regards to genetic risks, there is an increased incidence of myeloma [5] and monoclonal gammopathy [6] in the first-degree relatives of myeloma patients. Numerous incidents of environmental and occupational exposure have been implicated in the
E. E. Vokes et al. (eds.), Oncologic Therapies © Springer-Verlag Berlin Heidelberg 2003
etiology of myeloma, including agricultural, food processing, chemical, and petroleum products [7]. As with other hematologic malignancies, there is an increased risk noted with radiation exposure. The higher incidence of myeloma in atomic bomb survivors in Hiroshima and Nagasaki has been well documented [8] and excessive rates of myeloma in radiologist and nuclear power plant workers implicates the risk of low-level radiation exposure [9, 10]. Chronic antigenic stimulation has also been noted to be a predisposing state to myeloma [11], supporting a two hit-hypothesis in the genesis of this disease.
23.2 Pathology, Clinical Features, and Staging 23.2.1 Pathology 23.2.1.1 Morphology and Immunophenotyping The morphologic appearance of malignant and benign plasma cells is quite similar [12], containing a highly differentiated cytoplasm rich in rough endoplasmic reticulum [13]. The nucleus is typically eccentrically placed with clumped or diffuse chromatin, with a perinuclear clear zone, the site of the Golgi apparatus. Cell surface molecules that are characteristic on malignant plasma cells include CD19, CD38, and CD56 [14]. While several studies have demonstrated expression of myeloid, megakaryocytic, and erythroid surface markers not expressed on normal plasma cells [15], such aberrant expression is uncommon, and is associated with a poor prognosis.
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23.2.1.2 Cytogenetics Conventional cytogenetics in myeloma are limited because of the low rate of tumor cell proliferation. Aneuploidy, as assessed by cytogenetics or FISH (fluorescent in situ hyb
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