2026 ICD-10-CM Diagnosis Code C79.9Secondary malignant neoplasm of unspecified site
ICD-10-CM Codes›C00–D49›C76-C80›C79
- Billable — Valid for Submission
- Chronic Condition
C79.9 is a billable ICD-10-CM diagnosis code for secondary malignant neoplasm of unspecified site. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 826 through 830, 843 through 845. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Secondary malignancies.
Code Identity
Code Classification
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Anaplastic thyroid carcinoma
- Balloon cell malignant melanoma
- Complex mixed and stromal malignant neoplasm of endometrium of corpus uteri
- Distant metastasis present
- Embryonal rhabdomyosarcoma
- Endometrial stromal tumor
- Fibrosarcoma
- Ganglioneuroblastoma
- Germline BRCA-mutated, HER2-negative metastatic breast cancer
- HER2-positive carcinoma of breast
- Human epidermal growth factor 2 negative carcinoma of breast
- Infantile fibrosarcoma
- Intergroup rhabdomyosarcoma study post-surgical clinical group finding
- Intergroup rhabdomyosarcoma study post-surgical clinical group IV: Any size primary tumor, with or without regional lymph node involvement, with distant metastases, without respect to surgical approach to primary tumor
- Lentigo maligna melanoma
- Lymphedema due to malignant infiltration
- Malignant neoplasm of unknown origin
- Malignant tumor involving an organ by direct extension from bladder
- Malignant tumor involving an organ by direct extension from endometrium
- Malignant tumor involving an organ by direct extension from fallopian tube
- Malignant tumor involving an organ by direct extension from ovary
- Malignant tumor involving an organ by direct extension from prostate
- Malignant tumor involving an organ by direct extension from uterine cervix
- Malignant tumor involving an organ by direct extension from uterus
- Malignant tumor involving an organ by direct extension from vagina
- Metastatic acantholytic squamous cell carcinoma
- Metastatic adenocarcinoma
- Metastatic adenocarcinoma of unknown origin
- Metastatic adenosquamous carcinoma
- Metastatic anaplastic thyroid carcinoma
- Metastatic apocrine adenocarcinoma
- Metastatic balloon cell malignant melanoma
- Metastatic carcinoma to breast
- Metastatic castration-resistant prostate cancer
- Metastatic cholangiocarcinoma
- Metastatic clear cell renal cell carcinoma
- Metastatic collecting duct carcinoma
- Metastatic desmoplastic malignant melanoma
- Metastatic eccrine porocarcinoma
- Metastatic embryonal rhabdomyosarcoma
- Metastatic endometrial stromal sarcoma
- Metastatic extraskeletal osteosarcoma
- Metastatic fibrosarcoma
- Metastatic ganglioneuroblastoma
- Metastatic gastroesophageal adenocarcinoma
- Metastatic germinoma
- Metastatic glassy cell carcinoma
- Metastatic hepatocellular carcinoma
- Metastatic human epidermal growth factor 2 positive carcinoma of breast
- Metastatic infantile fibrosarcoma
- Metastatic inflammatory carcinoma
- Metastatic lentigo maligna melanoma
- Metastatic lobular carcinoma
- Metastatic lymphoepithelial carcinoma
- Metastatic malignant glioma
- Metastatic malignant melanoma
- Metastatic malignant melanoma to skin
- Metastatic malignant melanoma with diffuse hypermelanosis
- Metastatic malignant neoplasm
- Metastatic malignant neoplasm to thyroid gland
- Metastatic malignant neoplasm to unknown site
- Metastatic myxofibrosarcoma
- Metastatic neuroblastoma
- Metastatic oxyphilic adenocarcinoma
- Metastatic pancreatic endocrine carcinoma
- Metastatic papillary squamous cell carcinoma
- Metastatic penile cancer
- Metastatic pilomatrix carcinoma
- Metastatic pleomorphic rhabdomyosarcoma
- Metastatic renal cell carcinoma
- Metastatic rhabdomyosarcoma
- Metastatic sebaceous adenocarcinoma
- Metastatic small cell neuroendocrine carcinoma
- Metastatic spindle cell melanoma
- Metastatic spindle cell rhabdomyosarcoma
- Metastatic squamous cell carcinoma
- Metastatic superficial spreading melanoma
- Metastatic synovial sarcoma
- Metastatic urothelial carcinoma
- Metastatic well-differentiated neuroendocrine tumor
- Oligometastatic malignant neoplasm
- Oxyphilic adenocarcinoma
- Pachymeningitis
- Pachymeningitis due to secondary malignant neoplastic disease
- Pathologic fracture of bone at site of metastatic neoplasm
- Pleomorphic rhabdomyosarcoma
- Spindle cell malignant melanoma
- Spindle cell rhabdomyosarcoma
- Stage III: Extraglandular extension of tumor without other organ involvement
- Stage III: Macroscopic invasion of neighboring organs
- Stage IV: Distant metastasis or extension into other organs
- Stage IVb: Hematogenous or lymphatic dissemination
- Synovial sarcoma
- Thymic epithelial neoplasm stage finding
- Tumor invades beyond pancreatic capsule to adjacent structures AND/OR organs
- Tumor invasion by direct extension from organ of origin to adjacent organ
- Tumor invasion by direct extension to other structures
- Tumor invasion into adjacent tissues
- Tumor of unknown origin
Tabular List NotesGuidance
Coding notes and annotation back-references applicable to this code.
Inclusion Terms
- Metastatic cancer NOS
- Metastatic disease NOS
Type 1 Excludes
- carcinomatosis NOS C80.0
- generalized cancer NOS C80.0
- malignant primary neoplasm of unspecified site C80.1
These terms are the conditions for which that code is to be used. The terms may be synonyms of the code title, or, in the case of "other specified" codes, the terms are a list of the various conditions assigned to that code. The inclusion terms are not necessarily exhaustive. Additional terms found only in the Alphabetic Index may also be assigned to a code.
A type 1 excludes note is a pure excludes note. It means "NOT CODED HERE!" An Excludes1 note indicates that the code excluded should never be used at the same time as the code above the Excludes1 note. An Excludes1 is used when two conditions cannot occur together, such as a congenital form versus an acquired form of the same condition.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
- Disease, diseased - See Also: Syndrome;
- metastatic - See Also: Neoplasm, secondary, by site; - C79.9
- disease - See Also: Neoplasm, secondary, by site; - C79.9
External Cause of Injuries IndexGuidance
References for this code in the External Cause of Injuries Index.
- Disease, diseased
- metastatic
- Metastasis, metastatic
- disease
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Ganglioneuroblastoma
a moderately malignant neoplasm composed of primitive neuroectodermal cells dispersed in myxomatous or fibrous stroma intermixed with mature ganglion cells. it may undergo transformation into a neuroblastoma. it arises from the sympathetic trunk or less frequently from the adrenal medulla, cerebral cortex, and other locations. cervical ganglioneuroblastomas may be associated with horner syndrome and the tumor may occasionally secrete vasoactive intestinal peptide, resulting in chronic diarrhea.Dermatofibrosarcoma
a sarcoma of the deep layers of the skin. the tumors are locally aggressive tends to recur but rarely metastatic. it can be classified into variants depending on the cell type tumors are derived from or by its characteristics: pigmented variant from melanin-containing dermal dendritic cells; myxoid variant, myxoid stromal cells; giant cell variant characterized by giant cells in the tumors; and fibrosarcomatous variant chracterized by tumor areas histologically indistinguishable from fibrosarcoma.Fibrosarcoma
a sarcoma derived from deep fibrous tissue, characterized by bundles of immature proliferating fibroblasts with variable collagen formation, which tends to invade locally and metastasize by the bloodstream. (stedman, 25th ed)Horner Syndrome
a syndrome associated with defective sympathetic innervation to one side of the face, including the eye. clinical features include miosis; mild blepharoptosis; and hemifacial anhidrosis (decreased sweating)(see hypohidrosis). lesions of the brain stem; cervical spinal cord; first thoracic nerve root; apex of the lung; carotid artery; cavernous sinus; and apex of the orbit may cause this condition. (from miller et al., clinical neuro-ophthalmology, 4th ed, pp500-11)Localized Fibrosarcoma|Non-Metastatic Fibrosarcoma|Primary Fibrosarcoma
fibrosarcoma that is confined to a specific site without evidence of spread to other anatomic sites.Metastatic Fibrosarcoma
fibrosarcoma that has spread from its original site of growth to another anatomic site.Metastatic Myxofibrosarcoma
myxofibrosarcoma that has spread from its original site of growth to another anatomic site.Metastatic Hepatocellular Carcinoma
a hepatocellular carcinoma that has spread to another anatomic site.Metastatic Clear Cell Renal Cell Carcinoma
a clear cell renal cell carcinoma that has spread from its original site of growth to other anatomic sites.Metastatic Neuroblastoma
a neuroblastoma that has metastasized from its original site of growth to another anatomic site.Metastatic Rhabdomyosarcoma
rhabdomyosarcoma that has spread from its original site of growth to another anatomic site.Metastatic Embryonal Rhabdomyosarcoma
embryonal rhabdomyosarcoma that has spread from its original site of growth to another anatomic site.Metastatic Cholangiocarcinoma
a cholangiocarcinoma that has metastasized to other anatomic sites.
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 C79.9 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About C79.9Overview
Is C79.9 (Secondary malignant neoplasm of other and unspecified sites) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report secondary malignant neoplasm of unspecified site on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What MS-DRG does C79.9 group to?
When secondary malignant neoplasm of unspecified site is the principal diagnosis on an inpatient stay, it groups to MS-DRG 826, 827, 828, 829, 830, 843, 844, 845, with relative weights from 0.8516 to 4.6778 depending on complications. Higher weights mean higher Medicare reimbursement.
What is the ICD-9 equivalent of C79.9?
Under the General Equivalence Mappings, secondary malignant neoplasm of unspecified site converts to ICD-9-CM 198.89 (secondary malig neo NEC). The mapping is approximate, so confirm the match fits the documentation.
Footnotes
[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:
- The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
- The condition places limitations on self-care, independent living, and social interactions.
