All these criteria must be present:
- Biopsy proof of a plasma cell tumour
- No lytic bone lesions except the tumour itself
- Bone marrow plasma cell proportion less than 10%
- For solitary plasmacytoma of bone: no significant PET scan or CT scan abnormality at another site
A serum and/or urine monoclonal paraprotein may be present. Usually the uninvolved immunoglobulin levels are normal.