Surgical Pathology Criteria

Plasma Cell Myeloma

Differential Diagnosis

Plasmacytoma / Myeloma Reactive Plasmacytosis
Light chain restriction by flow cytometry, immunohistochemistry or in situ hybridization No light chain restriction

Plasmacytoma Myeloma
Single osseous or extraosseus lesion Lytic bony lesions
No increase away from lesion Usually increased plasma cells on random bone marrow biopsy
No end-organ damage May have end-organ damage

Symptomatic Plasma Cell Myeloma Asymptomatic / Smoldering Myeloma MGUS
Usually but not always >10% clonal plasma cells in bone marrow or plasmacytoma ** ≥10% clonal plasma cells in bone marrow AND/OR <10% clonal plasma cells in bone marrow
M protein in serum or urine or free light chain in urine Serum M-protein >3g/dL Serum M-protein <3g/dL
** Lytic bony lesions or  end-organ damage (hypercalcemia/ anemia/ renal insufficiency etc) No lytic lesions or end-organ damage No lytic lesions or end-organ damage
** Critical points: bone marrow plasma cells or M-protein above threshholds separates asymptomatic myeloma from MGUS and bone or other end organ damage separates symptomatic from asymptomatic myeloma

Plasmacytoma / Myeloma Lymphoplasmacytic Lymphoma and Nodal, Extranodal and Splenic Marginal Zone Lymphomas
Plasma cells may be pleomorphic or plasmablastic Plasma cell component usually not markedly atypical
Uniform plasma cell morphology Plasma cells mixed with small lymphocytes
IgG or IgA M component most common IgM or IgG M component most common
CD20 often negative CD20 80%
Uniformly CD138 positive Scattered CD138 positive cells
Often CD56+, CD19-, CD45- CD56-, CD19+, CD45+

Plasmablastic Lymphoma Anaplastic (Plasmablastic) Plasmacytoma/Myeloma
Plasmablastic morphology Subset plasmablastic
Often HIV+ or otherwise immunosuppressed Usually not immunosuppressed
Often in oral cavity or mucosal areas of head Extraosseous sites overlap
~60% EBV+ usually EBV negative
Plasmacytoma and plasmablastic lymphoma have the same immunophenotype, other than EBV and are generally separated based on clinical grounds

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