2027 ICD-10-CM Diagnosis Code C79.81Secondary malignant neoplasm of breast
ICD-10-CM Codes›C00–D49›C76-C80›C79
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Risk Adjusts — HCC 18
- Chronic Condition
C79.81 is a billable ICD-10-CM diagnosis code for secondary malignant neoplasm of breast. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 582 through 583, 597 through 599. 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 20 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Secondary malignancies.
For Medicare Advantage risk adjustment, C79.81 maps to CMS-HCC Category 18 (Cancer Metastatic to Bone, Other and Unspecified Metastatic Cancer; Acute Leukemia Except Myeloid) under the V28 model, adding a risk factor of about 2.341 for a community, non-dual, aged beneficiary in payment year 2027.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
C79.81 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.
- Adenocarcinoma of breast
- Bilateral metastatic malignant neoplasm to breasts
- Malignant neoplasm of areola
- Malignant neoplasm of bone, connective tissue, skin and breast
- Malignant neoplasm of ectopic site of breast
- Malignant neoplasm of nipple
- Metaplastic carcinoma of breast
- Metastatic carcinoma to axillary tail of breast
- Metastatic carcinoma to bone, connective tissue, skin and breast
- Metastatic carcinoma to breast
- Metastatic carcinoma to lower inner quadrant of breast
- Metastatic carcinoma to lower outer quadrant of breast
- Metastatic carcinoma to upper inner quadrant of breast
- Metastatic carcinoma to upper outer quadrant of breast
- Metastatic infiltrating duct carcinoma to breast
- Metastatic malignant neoplasm to areola
- Metastatic malignant neoplasm to axillary tail of breast
- Metastatic malignant neoplasm to breast
- Metastatic malignant neoplasm to central portion of breast
- Metastatic malignant neoplasm to ectopic site of breast
- Metastatic malignant neoplasm to left breast
- Metastatic malignant neoplasm to lower inner quadrant of breast
- Metastatic malignant neoplasm to lower outer quadrant of breast
- Metastatic malignant neoplasm to nipple
- Metastatic malignant neoplasm to right breast
- Metastatic malignant neoplasm to upper inner quadrant of breast
- Metastatic malignant neoplasm to upper outer quadrant of breast
- Metastatic metaplastic carcinoma to breast
- Metastatic scirrhous carcinoma to breast
- Neoplasm of areola
- Neoplasm of ectopic site of breast
- Scirrhous carcinoma of breast
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to C79.81: 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 C79.81, its category, or a range that includes it.
Applicable To 2
These notes mention C79.81.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Metastatic Malignant Neoplasm in the Breast
the spread of a malignant neoplasm to the breast. this may be from a primary breast malignant neoplasm on the opposite side, or from a malignant neoplasm at a distant site.
Table of NeoplasmsClinical
Anatomical sites in the Table of Neoplasms that reference this code family.
| Site | Malig. Primary | Malig. Secondary | Ca in situ | Benign | Uncertain | Unspec. |
|---|---|---|---|---|---|---|
| areola | C50.0 | C79.81 | D05. | D24. | D48.6 | D49.3 |
| breast (connective tissue) (glandular tissue) (soft parts) | C50.9 | C79.81 | D05. | D24. | D48.6 | D49.3 |
| breast (connective tissue) (glandular tissue) (soft parts) › areola | C50.0 | C79.81 | D05. | D24. | D48.6 | D49.3 |
| breast (connective tissue) (glandular tissue) (soft parts) › axillary tail | C50.6 | C79.81 | D05. | D24. | D48.6 | D49.3 |
| breast (connective tissue) (glandular tissue) (soft parts) › central portion | C50.1 | C79.81 | D05. | D24. | D48.6 | D49.3 |
| breast (connective tissue) (glandular tissue) (soft parts) › inner | C50.8 | C79.81 | D05. | D24. | D48.6 | D49.3 |
| breast (connective tissue) (glandular tissue) (soft parts) › lower | C50.8 | C79.81 | D05. | D24. | D48.6 | D49.3 |
| breast (connective tissue) (glandular tissue) (soft parts) › lower-inner quadrant | C50.3 | C79.81 | D05. | D24. | D48.6 | D49.3 |
| breast (connective tissue) (glandular tissue) (soft parts) › lower-outer quadrant | C50.5 | C79.81 | D05. | D24. | D48.6 | D49.3 |
| breast (connective tissue) (glandular tissue) (soft parts) › mastectomy site (skin) [See Also: Neoplasm, breast, skin] › specified as breast tissue | C50.8 | C79.81 | – | – | – | – |
| breast (connective tissue) (glandular tissue) (soft parts) › midline | C50.8 | C79.81 | D05. | D24. | D48.6 | D49.3 |
| breast (connective tissue) (glandular tissue) (soft parts) › nipple | C50.0 | C79.81 | D05. | D24. | D48.6 | D49.3 |
| breast (connective tissue) (glandular tissue) (soft parts) › outer | C50.8 | C79.81 | D05. | D24. | D48.6 | D49.3 |
| breast (connective tissue) (glandular tissue) (soft parts) › tail (axillary) | C50.6 | C79.81 | D05. | D24. | D48.6 | D49.3 |
| breast (connective tissue) (glandular tissue) (soft parts) › upper | C50.8 | C79.81 | D05. | D24. | D48.6 | D49.3 |
| breast (connective tissue) (glandular tissue) (soft parts) › upper-inner quadrant | C50.2 | C79.81 | D05. | D24. | D48.6 | D49.3 |
| breast (connective tissue) (glandular tissue) (soft parts) › upper-outer quadrant | C50.4 | C79.81 | D05. | D24. | D48.6 | D49.3 |
| mastectomy site (skin) [See Also: Neoplasm, breast, skin] › specified as breast tissue | C50.8 | C79.81 | – | – | – | – |
| nipple | C50.0 | C79.81 | D05. | D24. | – | – |
| skin NOS › mastectomy site (skin) [See Also: Neoplasm, skin, breast] › specified as breast tissue | C50.8 | C79.81 | – | – | – | – |
Patient EducationClinical
Breast Cancer
Breast cancer is a cancer that starts in breast tissue. It happens when cells in the breast change and grow out of control. New cells grow even when you don't need them, and old cells don't die when they should. These extra cells can form a mass called a tumor.
The full article covers:
- What is breast cancer?
- What are the types of breast cancer?
- What causes breast cancer?
- Who is at risk for breast cancer?
- What are the signs and symptoms of breast cancer?
- How is breast cancer diagnosed?
- What are the treatments for breast cancer?
- Can breast cancer be prevented?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert C79.81 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About C79.81Overview
What is the ICD-10 code for secondary malignant neoplasm of breast?
The ICD-10-CM code for secondary malignant neoplasm of breast is C79.81 (sometimes written as C7981). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is C79.81 (Secondary malignant neoplasm of other specified sites) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report secondary malignant neoplasm of breast on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does C79.81 group to?
When secondary malignant neoplasm of breast is the principal diagnosis on an inpatient stay, it groups to MS-DRG 598, 582, 599, 597, 583, with relative weights from 0.6756 to 1.8014 depending on complications. Higher weights mean higher Medicare reimbursement.
Is C79.81 a CC or MCC?
CMS lists C79.81 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 20 closely related codes in its exclusion list.
Can C79.81 be reported with a code from C7B?
Not as a rule. The Excludes1 note at C79, which applies to C79.81, 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 C79.81?
C79.81 (secondary malignant neoplasm of breast) maps to CMS-HCC Category 18 (Cancer Metastatic to Bone, Other and Unspecified Metastatic Cancer; Acute Leukemia Except Myeloid), commonly written as HCC 18, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It mapped to HCC 10 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 C79.81 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, C79.81 adds a risk adjustment factor of about 2.341 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 1.110 to 2.537 depending on the payment segment). A more severe related category (HCC 17) supersedes it when both are reported. See the full factor table on the HCC 18 category page.
