What is ICD-10 code C71.9?

C71.9 is the ICD-10-CM diagnosis code for Malignant neoplasm of brain, unspecified. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C71.9 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C71.9 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. C71.9 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. C71.9 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 C71.9 map to under V28?

C71.9 maps to CMS-HCC V28 HCC 20 (Lung and Other Severe Cancers). The category numbers, labels, and conditions come from the CMS-HCC V28 model file for payment year 2026.

What documentation supports C71.9?

Query the physician if more specific anatomical location is available, as codes C71.0-C71.8 provide more precise localization (cerebrum, cerebellum, brainstem, etc.) and may affect treatment planning and prognosis Ensure documentation includes whether this is a primary brain cancer or metastatic cancer that has spread to the brain, as metastatic cancers use different code categories (C79.31) For C71.9, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. See the MEAT criteria checklist at /meat-criteria for what Monitor, Evaluate, Assess, or Treat looks like in a note. One mnemonic element does not establish that a diagnosis is reportable.

2026 ICD-10-CM C71.9: Malignant neoplasm of brain

C71.9 maps to CMS-HCC V28 20. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · HCC coding software

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Code lookupC71.9

Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of eye, brain and other parts of central nervous system (C69-C72)

C71.9

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

Malignant neoplasm of brain, unspecified

This code represents a cancer that has started in the brain, but the specific location within the brain has not been identified or documented. It is used when a patient has been diagnosed with brain cancer without more detailed information about which part of the brain is affected.

Buddy Insight

This unspecified brain cancer code is used when a malignant brain tumor has been confirmed but the specific location within the brain has not been documented.

Overview Risk Models Code Book Documentation Audit Notes Edition comparison

CMS-HCC V28

Mapped

HCC 20

Lung and Other Severe Cancers

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 009

HHS-HCC 009 adult, RAF varies...

Code-level coefficient reference

ESRD/PACE

Mapped

HCC 10

Lymphoma and Other Cancers

Code-level coefficient reference

RXHCC

Mapped

HCC 22

Prostate, Breast, Bladder, an...

Code-level coefficient reference

Code Book Path

Official

C71Malignant neoplasm of brain C71.9Malignant neoplasm of brain, unspecified

Inclusion Terms

Official

No inclusion terms are included in this display for C71.9. Check the code and parent instructions in the Code Book.

Excludes 2

Official

No Excludes 2 notes are included in this display for C71.9. Check the code and parent instructions in the Code Book.

Related Codes

Official

C71.0Malignant neoplasm of cerebrum, except lobes and ventricles C71.1Malignant neoplasm of frontal lobe C71.2Malignant neoplasm of temporal lobe C71.3Malignant neoplasm of parietal lobe C71.4Malignant neoplasm of occipital lobe

Includes

Official

No Includes notes are included in this display for C71.9. Check the code and parent instructions in the Code Book.

Excludes 1

Official

malignant neoplasm of cranial nerves (C72.2-C72.5)Inherited from C71
retrobulbar malignant neoplasm (C69.6-)Inherited from C71

Code First

Official

No Code First sequencing instructions are included in this display for C71.9. Check the code and parent instructions in the Code Book.

Use Additional

Official

No Use Additional Code instructions are included in this display for C71.9. Check the code and parent instructions in the Code Book.

Code Also

Official

No Code Also instructions are included in this display for C71.9. Check the code and parent instructions in the Code Book.

Buddy Documentation Tip

HCC Buddy guidance

Confirmed malignant brain neoplasm by pathology or definitive imaging

Documentation that more specific location information was sought but unavailable

Evidence of provider query for specificity

Treatment status and clinical stage

MEAT Support

HCC Buddy guidance

Confirmed malignant brain neoplasm by pathology or definitive imaging

Documentation that more specific location information was sought but unavailable

Evidence of provider query for specificity

Treatment status and clinical stage

Audit Caution

HCC Buddy guidance

Defaulting to C71.9 without reviewing MRI or operative reports that almost always specify the brain region

Coding brain metastases as primary brain cancer (C71.9) instead of C79.31 — this is one of the most common coding errors in neuro-oncology

Using this code when pathology clearly identifies a lobe-specific tumor

Not recognizing that brain cancer specificity does not change HCC weight but does affect data quality and audit compliance

Common Mistakes

HCC Buddy guidance

C71.0-C71.8 — Specific brain location codes: always review imaging and surgical reports for location before defaulting to C71.9

C79.31 — Secondary brain malignancy: brain metastases from other cancers are extremely common and should not be coded as primary brain cancer

D43.2 — Brain neoplasm of uncertain behavior: use only when malignancy is not confirmed

D33.2 — Benign brain neoplasm: confirm malignant diagnosis before using C71 codes

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 C71.9 an HCC code?

Yes. C71.9 (Malignant neoplasm of brain, unspecified) maps to HCC 20, Lung and Other Severe Cancers under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 1.136. 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: C71.9 is billable and maps to V28 HCC 20, Lung and Other Severe Cancers. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: C71.9
Description: Malignant neoplasm of brain, unspecified
HCC (V28): HCC 20 — Lung and Other Severe Cancers
RAF reference coefficient: 1.136
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 20, Lung and Other Severe Cancers

1.136

ESRDHCC 10, Lymphoma and Other Cancers

Not separately weighted

RxHCCHCC 22, Prostate, Breast, Bladder, 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 C71.9 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT review for C71.9

For C71.9, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.

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

Coder workflow notes

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What This Code Means

C71.9 is the ICD-10-CM diagnosis code for malignant neoplasm of brain, unspecified. This code represents a cancer that has started in the brain, but the specific location within the brain has not been identified or documented. It is used when a patient has been diagnosed with brain cancer without more detailed information about which part of the brain is affected. C71.9 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of eye, brain and other parts of central nervous system (c69-c72).

Under the CMS-HCC V28 risk adjustment model, C71.9 maps to Lung and Other Severe Cancers (HCC 20) with a source-labeled community, non-dual, aged reference coefficient of 1.136. No V24 mapping is shown for C71.9; use the applicable model and payment year when reviewing the V28 mapping. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. 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.

Query the physician if more specific anatomical location is available, as codes C71.0-C71.8 provide more precise localization (cerebrum, cerebellum, brainstem, etc.) and may affect treatment planning and prognosis. For C71.9, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. 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 C71.9 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Query the physician if more specific anatomical location is available, as codes C71.0-C71.8 provide more precise localization (cerebrum, cerebellum, brainstem, etc.) and may affect treatment planning and prognosis
•Ensure documentation includes whether this is a primary brain cancer or metastatic cancer that has spread to the brain, as metastatic cancers use different code categories (C79.31)

Clinical Significance

This unspecified brain cancer code is used when a malignant brain tumor has been confirmed but the specific location within the brain has not been documented. While it captures the cancer diagnosis for risk adjustment at the same HCC weight, it represents a significant documentation gap given that MRI or surgical reports nearly always identify the tumor location.

Documentation Requirements

✓Confirmed malignant brain neoplasm by pathology or definitive imaging
✓Documentation that more specific location information was sought but unavailable
✓Evidence of provider query for specificity
✓Treatment status and clinical stage
✓Histological type if pathology has been performed

Commonly Confused Codes

•C71.0-C71.8: Specific brain location codes: always review imaging and surgical reports for location before defaulting to C71.9
•C79.31: Secondary brain malignancy: brain metastases from other cancers are extremely common and should not be coded as primary brain cancer
•D43.2: Brain neoplasm of uncertain behavior: use only when malignancy is not confirmed
•D33.2: Benign brain neoplasm: confirm malignant diagnosis before using C71 codes