C80.1
BillableMalignant (primary) neoplasm, unspecified
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C80.1 an HCC code?
Yes. C80.1 maps to Melanoma and Other Skin Cancers under the CMS-HCC V28 risk adjustment model (and Breast, Prostate, and Other Cancers and Tumors 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 C80.1
For C80.1 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 C80.1 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C80.1 is the ICD-10-CM diagnosis code for malignant (primary) neoplasm, unspecified. A cancer diagnosis where the specific type and location of the original tumor cannot be determined or identified. C80.1 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of ill-defined, other secondary and unspecified sites (c76-c80).
Under the CMS-HCC V28 risk adjustment model, C80.1 maps to Melanoma and Other Skin Cancers (HCC 23) with a community, non-dual, aged base RAF weight of 0.251. Under the older CMS-HCC V24 model, C80.1 maps to Breast, Prostate, and Other Cancers and Tumors (HCC 12) with a community, non-dual, aged base RAF weight of 0.150. 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 a last-resort code when no other cancer code can be determined from documentation. Because C80.1 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 C80.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This is a last-resort code when no other cancer code can be determined from documentation
- •Investigate medical records thoroughly before assigning this non-specific code
Clinical Significance
Malignant (primary) neoplasm, unspecified indicates a confirmed cancer diagnosis where the primary site and specific cancer type cannot be determined. This is a last-resort code used only when thorough investigation fails to identify the tumor origin. Cancer of unknown primary accounts for 3-5% of all cancer diagnoses and typically presents as metastatic disease with an unidentifiable primary site despite comprehensive diagnostic workup.
Documentation Requirements
- ✓Physician documentation confirming active malignancy
- ✓Record of diagnostic workup attempted (imaging, biopsies, tumor markers)
- ✓Explanation for why primary site cannot be identified
- ✓Documentation that the cancer is primary (not secondary/metastatic to the organ biopsied)
- ✓Treatment plan (empiric chemotherapy, palliative care)
- ✓Performance status and functional assessment
Excludes 1 — Do NOT code together
- secondary malignant neoplasm of unspecified site (C79.9)