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WHO Classification of Tumours
Monoclonal gammopathy of undetermined significance
Tumours of haematopoietic and lymphoid tissues


MGUS is defined as the presence in the serum of an M-protein <30 g/L, bone marrow (BM) clonal plasma cells <10%, no end organ damage (CRAB: hypercalcemia, renal insufficiency, anaemia, bone lesions) and no evidence of B-cell lymphoma or other disease known to produce an M-protein (Table 10.04). Although it reflects the presence of an expanded clone of immunoglobulin-secreting cells, this process is not considered neoplastic since it does not always progress to overt malignancy. The presence of a small IgM paraprotein (IgM MGUS) is associated with a clone of lymphoplasmacytic cells that may progress to a lymphoplasmacytic lymphoma and/ or Waldenström macroglobulinemia (WM). Non-IgM MGUS (IgG, IgA) is associated with the presence of clonal plasma cells, and may progress to a malignant plasma cell neoplasm. Although the two forms of MGUS may be identical in their clinical presentation, they have a different genetic basis and different outcomes in terms of malignant progression.

> Related Topics
Definition: Plasma cell neoplasms
Introduction: Classification of lymphoid neoplasms