C79.31 ICD-10-CM Code: Secondary malignant neoplasm of brain
HCC Buddy Code Card
Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.
FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of ill-defined, other secondary and unspecified sites (C76-C80)
C79.31
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceSecondary malignant neoplasm of brain
Cancer that has spread to the brain tissue itself from a primary cancer located elsewhere in the body.
Buddy Insight
Secondary malignant neoplasm of the brain is a devastating complication of advanced cancer, significantly impacting neurological function, quality of life, and survival.
CMS-HCC V28
MappedHCC 17
RAF 0.368
CMS-HCC V24
MappedHCC 8
RAF 2.484
ACA/HHS
00
RAF 0
ESRD/PACE
MappedHCC 8
RAF 0.0
RXHCC
MappedHCC 18
RAF 0.0
Code Trumping
Basket needed
Code Book Path
Inclusion Terms
OfficialICD-10-CM does not list inclusion terms for C79.31 in this effective period.
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for C79.31 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for C79.31 in this effective period.
Excludes 1
OfficialICD-10-CM does not list Excludes 1 notes for C79.31 in this effective period.
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for C79.31 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for C79.31 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for C79.31 in this effective period.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.
Is C79.31 an HCC code?
Yes. C79.31 maps to Metastatic Cancer and Acute Leukemia under the CMS-HCC V28 risk adjustment model (and Metastatic Cancer and Acute Leukemia 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 C79.31
For C79.31to 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 C79.31 during that encounter, not just copy-forwarded from a problem list.
What This Code Means
C79.31 is the ICD-10-CM diagnosis code for secondary malignant neoplasm of brain. Cancer that has spread to the brain tissue itself from a primary cancer located elsewhere in the body. C79.31 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, C79.31 maps to Metastatic Cancer and Acute Leukemia (HCC 17) with a community, non-dual, aged base RAF weight of 0.368. Under the older V24 model, C79.31 mapped to the same category but with a base RAF weight of 2.484, 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.
Distinguish between brain metastases (C79.31) and meningeal metastases (C79.32); brain tissue involvement versus membrane involvement requires different codes. Because C79.31 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 C79.31 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Distinguish between brain metastases (C79.31) and meningeal metastases (C79.32); brain tissue involvement versus membrane involvement requires different codes
- •Brain metastases are a serious complication requiring coordination with oncology and neurology; ensure primary cancer site is documented
Clinical Significance
Secondary malignant neoplasm of the brain is a devastating complication of advanced cancer, significantly impacting neurological function, quality of life, and survival. Brain metastases are common in lung, breast, melanoma, and renal cell cancers. Treatment requires multidisciplinary coordination involving neurosurgery, radiation oncology, and medical oncology, and these patients have high resource utilization.
Documentation Requirements
- ✓Primary cancer site documented and coded separately
- ✓Imaging confirmation — brain MRI with contrast is the gold standard
- ✓Number, size, and location of brain metastases (supratentorial vs. infratentorial)
- ✓Neurological symptoms — headache, seizures, focal deficits, cognitive changes
- ✓Treatment approach — surgical resection, stereotactic radiosurgery, whole-brain radiation, systemic therapy
- ✓Presence of cerebral edema or mass effect requiring additional coding
Commonly Confused Codes
- •C79.32 — Secondary malignant neoplasm of cerebral meninges; brain parenchymal involvement (C79.31) is different from meningeal involvement (C79.32)
- •C71.0-C71.9 — Primary malignant neoplasm of brain; primary brain tumors (gliomas, etc.) are different from brain metastases
- •C79.40 — Secondary malignant neoplasm of unspecified nervous system; use C79.31 when brain is specifically documented
- •G93.6 — Cerebral edema; may occur secondary to brain metastases and should be coded separately