Plasmacytoma
Differential Diagnosis
| 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 |
| Plasmacytoma / Myeloma |
Reactive Plasmacytosis |
| Light chain restriction by flow cytometry, immunohistochemistry or in situ hybridization |
No light chain restriction |
| 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
| 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+ |
| ALK Positive Large B Cell Lymphoma |
Plasmacytoma |
| ALK positive |
ALK negative |
| Often involves nodes in sinusoidal pattern |
No sinusoidal node involvement |
| Usually presents with adenopathy without lytic bone lesions |
Usually presents with lytic bone lesions without adenopathy |
| No M component |
May have M component |
| May show ALK-clathrin translocation t(2;17)(p23;q23) |
Lacks this translocation |
Both may have basophilic cytoplasm with a perinuclear hof
| Primary Effusion Lymphoma |
Plasmacytoma |
| HHV8 positive |
HHV8 negative |
| EBV in situ positive |
EBV in situ infrequently positive |
| Most patients HIV positive |
No significant HIV predilection |
| Usually presents as malignant effusion |
Usually presents as lytic bone lesion |
PEL may rarely occur outside of body cavities; both may have plasmablastic appearance
