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