2027 ICD-10-CM Diagnosis Code C79.40Secondary malignant neoplasm of unspecified part of nervous system
ICD-10-CM Codes›C00–D49›C76-C80›C79
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Risk Adjusts — HCC 17
- Chronic Condition
C79.40 is a billable ICD-10-CM diagnosis code for secondary malignant neoplasm of unspecified part of nervous system. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 54 through 55. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 22 closely related codes. Coders also document this condition as metastasis to peripheral nerve. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Secondary malignancies.
For Medicare Advantage risk adjustment, C79.40 maps to CMS-HCC Category 17 (Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic) under the V28 model, adding a risk factor of about 4.209 for a community, non-dual, aged beneficiary in payment year 2027.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
C79.40 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2027.
Source: CMS Payment Year 2027 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Metastasis to peripheral nerve
- Metastatic malignant neoplasm to central nervous system
- Metastatic malignant neoplasm to nervous system
- Metastatic neuroblastoma
- Metastatic neuroblastoma to central nervous system
- Neuroblastoma of central nervous system
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to C79.40: its own notes plus those printed at C79 and Chapter 2. A note printed at a category, block or chapter applies to every code under it.
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
Notes
General instructions on how these codes are used.
- Functional activity
- All neoplasms are classified in this chapter, whether they are functionally active or not. An additional code from Chapter 4 may be used, to identify functional activity associated with any neoplasm.
- Morphology [Histology]
- Chapter 2 classifies neoplasms primarily by site (topography), with broad groupings for behavior, malignant, in situ, benign, etc. The Table of Neoplasms should be used to identify the correct topography code. In a few cases, such as for malignant melanoma and certain neuroendocrine tumors, the morphology (histologic type) is included in the category and codes.
- Primary malignant neoplasms overlapping site boundaries
- A primary malignant neoplasm that overlaps two or more contiguous (next to each other) sites should be classified to the subcategory/code .8 ('overlapping lesion'), unless the combination is specifically indexed elsewhere. For multiple neoplasms of the same site that are not contiguous, such as tumors in different quadrants of the same breast, codes for each site should be assigned.
- Malignant neoplasm of ectopic tissue
- Malignant neoplasms of ectopic tissue are to be coded to the site mentioned, e.g., ectopic pancreatic malignant neoplasms are coded to pancreas, unspecified (C25.9).
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name C79.40, its category, or a range that includes it.
Applicable To 2
These notes mention C79.40.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Metastatic Malignant Neoplasm in the Nervous System
the spread of a malignant neoplasm to the nervous system. this may be from a primary nervous system malignant neoplasm, or from a malignant neoplasm at a distant site.
Table of NeoplasmsClinical
Patient EducationClinical
Cancer
Cancer is not just one disease but many diseases. Cancer begins in your cells, which are the building blocks of your body. Usually, your body forms new cells as needed, replacing old cells that die. Sometimes this process goes wrong. New cells grow even when you don't need them, and old cells don't die when they should.
The full article covers:
- What is cancer?
- What are the types of cancer?
- How does cancer develop?
- What are the symptoms of cancer?
- How is cancer diagnosed?
- What are the treatments for cancer?
- Can cancer be prevented?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert C79.40 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About C79.40Overview
What is the ICD-10 code for secondary malignant neoplasm of unspecified part of nervous system?
The ICD-10-CM code for secondary malignant neoplasm of unspecified part of nervous system is C79.40 (sometimes written as C7940). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is C79.40 a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report secondary malignant neoplasm of unspecified part of nervous system on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does C79.40 group to?
When secondary malignant neoplasm of unspecified part of nervous system is the principal diagnosis on an inpatient stay, it groups to MS-DRG 55, 54, with relative weights from 1.0291 to 1.5197 depending on complications. Higher weights mean higher Medicare reimbursement.
Is C79.40 a CC or MCC?
CMS lists C79.40 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 22 closely related codes in its exclusion list.
Can C79.40 be reported with a code from C7B?
Not as a rule. The Excludes1 note at C79, which applies to C79.40, lists "secondary carcinoid tumors (C7B.-)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).
What HCC is C79.40?
C79.40 (secondary malignant neoplasm of unspecified part of nervous system) maps to CMS-HCC Category 17 (Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic), commonly written as HCC 17, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It mapped to HCC 8 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. In the Part D prescription drug model it maps to RxHCC 18.
Does C79.40 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, C79.40 adds a risk adjustment factor of about 4.209 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 1.952 to 4.235 depending on the payment segment). HCC 17 sits at the top of its hierarchy, so no other condition category supersedes it. See the full factor table on the HCC 17 category page.
