C41.9
BillableMalignant neoplasm of bone and articular cartilage, unspecified
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C41.9 an HCC code?
Yes. C41.9 maps to Lymphoma and Other Cancers under the CMS-HCC V28 risk adjustment model (and Lymphoma and Other Cancers under V24).
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. 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.
MEAT Criteria for C41.9
For C41.9to 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 C41.9 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C41.9 is the ICD-10-CM diagnosis code for malignant neoplasm of bone and articular cartilage, unspecified. Cancer of bone or cartilage when the specific bone location is not identified or specified. C41.9 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of bone and articular cartilage (c40-c41).
Under the CMS-HCC V28 risk adjustment model, C41.9 maps to Lymphoma and Other Cancers (HCC 21) with a community, non-dual, aged base RAF weight of 0.671. Under the older V24 model, C41.9 mapped to the same category but with a base RAF weight of 0.675 — V28 recalibrated weights across the entire model. 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.
This is the least specific bone cancer code; use only when no other information is available. Because C41.9 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 C41.9 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This is the least specific bone cancer code; use only when no other information is available
- •Always query provider for more specific anatomical location to allow for more precise coding
Clinical Significance
Primary malignant neoplasm of bone and articular cartilage, unspecified site. This is the most nonspecific code in the bone malignancy category and should only be used when the anatomic site truly cannot be determined. This code should trigger a provider query for more specific site information to improve documentation quality and audit defensibility.
Documentation Requirements
- ✓Provider query for specific bone site — this code represents documentation failure
- ✓Histologic confirmation of malignancy
- ✓Primary vs. metastatic origin confirmed
- ✓Any imaging available that could identify the bone site
- ✓Clinical rationale for why the site cannot be specified
- ✓Treatment plan and disease status
Commonly Confused Codes
- •C40.90 — Unspecified bones of unspecified limb; use when it is at least known to be a limb bone
- •C41.0 through C41.4 — Specific axial skeleton sites; always preferred over C41.9
- •C79.51 — Secondary malignant neoplasm of bone; for metastatic disease, not primary
- •D49.2 — Neoplasm of unspecified behavior of bone; when malignancy is not yet confirmed