Plasmacytoma

2016 WHO Classification
  • Solitary Plasmacytoma of Bone
  • Extra-osseous Plasmacytoma


Solitary Plasmacytoma of Bone
  • Modest elevations of M protein in serum or urine in a subset of patients (24-72%).
  • Localized collection of monoclonal plasma cells (plasmacytoma), without evidence of systemic disease.
    • Normal random bone marrow biopsy without clonal plasma cells.
    • Normal skeletal survey and MRI or CT
    • Abence of end organ damage (defines multiple myeloma)
  • Osseous plasmacytomas have a very high risk of progressing to multiple myeloma (though this can take up to 20 years or longer).
    • Up to 2/3rds will progress
    • 10% will progress within 3 years

Solitary Plasmacytoma with minimal bone marrow involvement – is defined by <10% clonal plasma cells in a random bone marrow biopsy.  Approximately 60% of these patients will progress to plasma cell myeloma in 3 years.


Extra-osseous Plasmacytoma
  • Modest elevations of M protein in serum or urine (often IgA) in a subset of patients (20%).
  • Localized collection of monoclonal plasma cells (plasmacytoma), without evidence of systemic disease.
    • Normal random bone marrow biopsy without clonal plasma cells.
    • Normal skeletal survey and MRI or CT
    • Absence of end organ damage (defines multiple myeloma)
  • Non-osseous plasmacytomas have a very low risk of progressing to multiple myeloma (~15%) and are often cured by local excision or radiation (~25% regional recurrence rate).
  • May be challenging to differentiate from a lymphoma with prominent plasmacytic differentiation
    • Atypical/blastic appearance would favor a multiple myeloma or plasmablastic lymphoma.
    • Evidence of a monoclonal lymphoid population (flow cytometry) would support a lymphoma with plasmacytic differentiation.
    • Sometimes it is not possible to definitively differentiate between a plasmacytoma and lymphoma with plasmacytic differentiation.
  • Immunophenotype
    • Cyclin D1 – Negative
    • CD56 – ~1/3rd may have weak expression (multiple myeloma – 71%+)
    • CD45 – 91% positive (multiple myeloma – 41%+)
    • CD19 – 95% positive (multiple myeloma – 10%+)

References
Robbins and Cotran Pathologic Basis of Disease.  V Kumar, et al. 9th Edition. Elsevier Saunders. 2015. pp. 599-601.
 
WHO Classification of Tumors of Haematopoietic and Lymphoid Tissues.  SH Swerdlow, et al. International Agency for Research on Cancer. Lyon, 2008.  pp. 200-213
 
Swerdlow SH, Campo E, Pileri SA, Harris NL, Stein H, Siebert R, et al. The 2016 revision of the World Health Organization classification of lymphoid neoplasms. Blood. 2016;127: 2375–2390. doi:10.1182/blood-2016-01-643569