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C90.21 ICD-10-CM Code: Extramedullary plasmacytoma in remission

C90.21 maps to CMS-HCC V28 19 (RAF 1.798). Documentation must support MEAT. MEAT criteria · RAF calculator · free HCC coding tools

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FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of lymphoid, hematopoietic and related tissue (C81-C96)

C90.21

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Extramedullary plasmacytoma in remission

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

Buddy the Bee presenting code insight

Buddy Insight

Extramedullary plasmacytoma in remission indicates successful treatment of this localized plasma cell tumor, typically achieved through radiation therapy.

CMS-HCC V28

HCC 19

RAF 1.798

CMS-HCC V24

HCC 9

RAF 1.024

ACA/HHS

HCC 9

Varies by metal level

ESRD/PACE

HCC 9

RAF 0.181

RXHCC

HCC 16

RAF 14.205

Code Book Path

Official
C90Multiple myeloma and malignant plasma cell neoplasms
C90.2Extramedullary plasmacytoma
C90.21Extramedullary plasmacytoma in remission

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for C90.21 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C90.21 in this effective period.

Related Child Codes

Official
C90.20Extramedullary plasmacytoma not having achieved remission
C90.22Extramedullary plasmacytoma in relapse

Includes

Official

ICD-10-CM does not list Includes notes for C90.21 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for C90.21 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C90.21 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C90.21 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C90.21 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance
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.

MEAT Support

HCC Buddy guidance
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.

Audit Caution

HCC Buddy guidance
Do not assign remission without imaging and clinical confirmation from the treating physician.
Continue monitoring for progression to multiple myeloma even in remission.
This remains an active malignancy code requiring surveillance, not a history code.

Common Mistakes

HCC Buddy guidance
C90.20 (extramedullary plasmacytoma not in remission) indicates active disease.
C90.22 (extramedullary plasmacytoma in relapse) indicates recurrence.
C90.01 (multiple myeloma in remission) would be appropriate if the disease has evolved to systemic myeloma.
Z85.79 is only for cured disease no longer under surveillance.

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is C90.21 an HCC code?

Yes. C90.21 (Extramedullary plasmacytoma in remission) maps to Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers under the CMS-HCC V28 risk adjustment model (and Lung and Other Severe Cancers under V24), with a community non-dual aged RAF of 1.798. It is billable for payment year 2026.

Coder answer: C90.21 is billable and maps to V28 HCC 19, Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code
C90.21
Description
Extramedullary plasmacytoma in remission
HCC (V28)
HCC 19 — Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers
RAF
1.798
Billable
Yes
Payment year
2026

HCC Category Mapping

V28HCC 19, Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers
1.798
V24HCC 9, Lung and Other Severe Cancers
1.024
ESRDHCC 9, Lung and Other Severe Cancers
0.181
RxHCCHCC 16, Multiple Myeloma and Plasma Cell Neoplasms
14.205

Each model's RAF is its CMS base weight for that model's standard population, so weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.

Work C90.21 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for C90.21

For C90.21 to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically, it has to be re-documented and supported each calendar year.

  • MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
  • EEvaluate: test results, medication response, or physical findings reviewed by the provider
  • AAssess: explicit mention in the assessment or plan with acknowledgment of status
  • TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis

Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed C90.21 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

C90.21 is the ICD-10-CM diagnosis code for extramedullary plasmacytoma in remission. A rare cancer of plasma cells located outside the bone marrow that is currently in remission (no signs of active disease). C90.21 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of lymphoid, hematopoietic and related tissue (c81-c96).

Under the CMS-HCC V28 risk adjustment model, C90.21 maps to Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers (HCC 19) with a community, non-dual, aged base RAF weight of 1.798. Under the older CMS-HCC V24 model, C90.21 maps to Lung and Other Severe Cancers (HCC 9) with a community, non-dual, aged base RAF weight of 1.024. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.

Remission status must be documented in the medical record; do not assume remission without explicit physician statement. Because C90.21 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.

HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for C90.21 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

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

  • •C90.20 (extramedullary plasmacytoma not in remission) indicates active disease.
  • •C90.22 (extramedullary plasmacytoma in relapse) indicates recurrence.
  • •C90.01 (multiple myeloma in remission) would be appropriate if the disease has evolved to systemic myeloma.
  • •Z85.79 is only for cured disease no longer under surveillance.

Child Codes

C90.20Extramedullary plasmacytoma not having achieved remission
HCC 19
C90.21Extramedullary plasmacytoma in remission
HCC 19
C90.22Extramedullary plasmacytoma in relapse
HCC 19

Code Hierarchy

└C90Multiple myeloma and malignant plasma cell neoplasms└C90.2Extramedullary plasmacytoma└C90.21Extramedullary plasmacytoma in remission
└C90.21Extramedullary plasmacytoma in remission

Because C90.21 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

C90.21 maps to CMS-HCC V28 category 19, Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works. Because C90.21 carries a payment HCC, you can see what it adds to a RAF score and check the documentation the chart needs before it is submitted.

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Open C90.21 in the Code Book for the full Index-to-Tabular path, MEAT checklist, and V28 HCC mapping, or in the Encoder to code from a keyword search. Pro includes 7 days to try everything, no card required.

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