What is ICD-10 code C80.1?

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. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C80.1 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C80.1 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. C80.1 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. C80.1 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

Which HCC does C80.1 map to under V28?

C80.1 maps to CMS-HCC V28 HCC 23 (Prostate, Breast, and Other Cancers and Tumors). The category numbers, labels, and conditions come from the CMS-HCC V28 model file for payment year 2026.

2026 ICD-10-CM C80.1: Malignant (primary) neoplasm

C80.1 maps to CMS-HCC V28 23. A source-labeled RAF reference is available. Documentation must support MEAT. MEAT criteria · RAF Calculator · free HCC coding tools

ICD-10-CM Code View

HCC Buddy Code Card

Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.

Code lookupC80.1Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of ill-defined, other secondary and unspecified sites (C76-C80)

C80.1

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

Malignant (primary) neoplasm, unspecified

A cancer diagnosis where the specific type and location of the original tumor cannot be determined or identified.

Buddy Insight

Malignant (primary) neoplasm, unspecified indicates a confirmed cancer diagnosis where the primary site and specific cancer type cannot be determined.

CMS-HCC V28

Mapped

HCC 23

Prostate, Breast, and Other C...

Code-level coefficient reference

CMS-HCC V24

Historical

Not used for standard CY2026 Medicare Advantage payment. Select a historical period to review V24.

Not used for CY2026 payment

ACA/HHS

Mapped

HCC 013

HHS-HCC 013 adult, RAF varies...

Code-level coefficient reference

ESRD/PACE

Mapped

HCC 12

Breast/Prostate/and Other Can...

Code-level coefficient reference

RXHCC

N/A

—

Not risk-adjusted for this model/period.

Not mapped

Code Book Path

Official

C80Malignant neoplasm without specification of site

C80.1Malignant (primary) neoplasm, unspecified

Inclusion Terms

Official

Cancer NOS
Cancer unspecified site (primary)
Carcinoma unspecified site (primary)
Malignancy unspecified site (primary)

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C80.1 in this effective period.

Related Child Codes

Official

C80.0Disseminated malignant neoplasm, unspecified

C80.2Malignant neoplasm associated with transplanted organ

Includes

Official

ICD-10-CM does not list Includes notes for C80.1 in this effective period.

Excludes 1

Official

secondary malignant neoplasm of unspecified site (C79.9)

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C80.1 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C80.1 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C80.1 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

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)

MEAT Support

HCC Buddy guidance

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)

Audit Caution

HCC Buddy guidance

Using C80.1 when the primary site is actually documented elsewhere in the medical record — always check oncology notes, pathology, and imaging

Assigning this code for a known cancer type before completing a thorough chart review

Confusing active unspecified malignancy with history of cancer (Z85 codes)

Not querying the provider for additional information that might allow a more specific code assignment

Common Mistakes

HCC Buddy guidance

C80.0 — Disseminated malignant neoplasm, unspecified: Use when cancer is confirmed to be widespread/disseminated; C80.1 does not imply dissemination

C80.2 — Malignant neoplasm associated with transplanted organ: Use when cancer arises in or is related to a transplanted organ

D49.9 — Neoplasm of unspecified behavior, unspecified site: Use when it is unclear whether the neoplasm is benign or malignant

Z85 series — Personal history of malignant neoplasm: Use when cancer has been treated and is in the patient's history, not actively present

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 C80.1 an HCC code?

Yes. C80.1 (Malignant (primary) neoplasm, unspecified) maps to HCC 23, Prostate, Breast, and Other Cancers and Tumors under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.186. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.

Coder answer: C80.1 is billable and maps to V28 HCC 23, Prostate, Breast, and Other Cancers and Tumors. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: C80.1
Description: Malignant (primary) neoplasm, unspecified
HCC (V28): HCC 23 — Prostate, Breast, and Other Cancers and Tumors
RAF reference coefficient: 0.186
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 23, Prostate, Breast, and Other Cancers and Tumors

0.186

ESRDHCC 12, Breast/Prostate/and Other Cancers and Tumors

Not separately weighted

These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. 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 context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.

Work C80.1 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

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.

Coder workflow notes

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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 Prostate, Breast, and Other Cancers and Tumors (HCC 23) with a source-labeled community, non-dual, aged reference coefficient of 0.186. No V24 mapping is shown for C80.1; use the applicable model and payment year when reviewing the V28 mapping. 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. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.

This is a last-resort code when no other cancer code can be determined from documentation. Because C80.1 maps to an HCC category, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) before the diagnosis is used for risk adjustment. 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, source-labeled coefficient references, 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)

Commonly Confused Codes

•C80.0: Disseminated malignant neoplasm, unspecified: Use when cancer is confirmed to be widespread/disseminated; C80.1 does not imply dissemination
•C80.2: Malignant neoplasm associated with transplanted organ: Use when cancer arises in or is related to a transplanted organ
•D49.9: Neoplasm of unspecified behavior, unspecified site: Use when it is unclear whether the neoplasm is benign or malignant
•Z85 series: Personal history of malignant neoplasm: Use when cancer has been treated and is in the patient's history, not actively present