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Plasma cell neoplasms are monoclonal expansions of plasma cells and their precursors. These often can be detected and monitored by evaluating the levels of monoclonal immunoglobulin or immunoglobulin chains in the plasma or urine. Rapidly progressive plasma cell neoplasms often present with evidence of organ dysfunction or have a much higher potential for organ dysfunction. On the other hand, patients with nonprogressive or slowly progressive essential monoclonal gammopathy can live for many years with no evidence of disease except for abnormalities on laboratory tests. Moreover, although monoclonal immunoglobulin protein generally is detected in plasma cell myeloma, other conditions also may result in production of monoclonal immunoglobulin. This chapter summarizes the laboratory studies used to evaluate for monoclonal immunoglobulins or monoclonal immunoglobulin gene rearrangements; delineates laboratory features that can help distinguish plasma cell myeloma from related conditions that may also be associated with a monoclonal immunoglobulin; and provides references to relevant chapters in the textbook that focus on a particular plasma cell or B-cell disorders.

Acronyms and Abbreviations

Acronyms and abbreviations that appear in this chapter include: CAS, cold agglutinin syndrome; CSF, cerebrospinal fluid; HLA, human leukocyte antigen; Ig, immunoglobulin; IL, interleukin; PCN, plasma cell neoplasm; PCR, polymerase chain reaction; TNF, tumor necrosis factor.

Plasma Cell Neoplasms

Plasma cell neoplasms (PCNs) are monoclonal expansions of a single B lymphocyte characterized by plasma cell morphology and monoclonal immunoglobulin gene rearrangement. The vast majority of PCNs produce monoclonal immunoglobulin or immunoglobulin fragments. For such PCNs, the cells within the neoplasm produce the same whole immunoglobulin chain or chain fragment. In a given neoplasm, the monoclonal proteins generally have the same heavy-chain class/isotype (γ, α, μ, δ, or ε), same light-chain class (κ or λ), and same idiotypes (or antigenic determinants of the immunoglobulin variable regions; see Chap. 77).1 The neoplastic plasma cells also share chromosomal anomalies, if any are present,2 although clonal evolution may occur as the disease progresses (see Chap. 109). Since Henry Bence Jones3 first discovered what turned out to be monoclonal light chains in the urine of myeloma patients more than 160 years ago, the monoclonal immunoglobulin molecules (or their constituent chains) produced by plasma cell neoplasms have remained the best examples of tumor-specific antigens in the field of oncology. These proteins usually are called M proteins, which at various times in history has stood for malignant, myeloma, and now monoclonal proteins. Table 107–1 lists the diseases associated with M proteins. Some of the diseases are nonprogressive or very slowly progressive, whereas some are malignant and more rapidly progressive, causing disease and organ damage.

Table 107–1. Diseases Associated with M Proteins

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