C90.21

HCC Category Mapping

What This Code Means

A rare cancer of plasma cells located outside the bone marrow that is currently in remission (no signs of active disease).

Coding Tips

• •Remission status must be documented in the medical record; do not assume remission without explicit physician statement
• •This code is specific to extramedullary location; verify the plasmacytoma is not in bone marrow before assigning

Clinical Significance

Extramedullary plasmacytoma in remission indicates successful treatment of this localized plasma cell tumor, typically achieved through radiation therapy. The prognosis for remission in extramedullary plasmacytoma is generally favorable, but long-term surveillance is needed to detect local recurrence or possible progression to multiple myeloma, which occurs in approximately 15% of cases over 10 years.

Documentation Requirements

• ✓Provider must document remission status explicitly, supported by imaging showing resolution of the tumor mass and normalization of any previously abnormal protein studies.
• ✓Surveillance imaging schedule, periodic bone marrow biopsy and protein electrophoresis for myeloma screening, and the original extramedullary location must be documented.

Commonly Confused Codes