2024 ICD-10-CM Diagnosis Code C79.9

Secondary malignant neoplasm of unspecified site

ICD-10-CM Code:
ICD-10 Code for:
Secondary malignant neoplasm of unspecified site
Is Billable?
Yes - Valid for Submission
Chronic Condition Indicator: [1]
Code Navigator:

Code Classification

  • Neoplasms
    • Malignant neoplasms of ill-defined, other secondary and unspecified sites
      • Secondary malignant neoplasm of other and unspecified sites

C79.9 is a billable diagnosis code used to specify a medical diagnosis of secondary malignant neoplasm of unspecified site. The code is valid during the current fiscal year for the submission of HIPAA-covered transactions from October 01, 2023 through September 30, 2024.

The following anatomical sites found in the Table of Neoplasms reference this diagnosis code given the correct histological behavior: Neoplasm, neoplastic metastatic NEC [See Also: Neoplasm, by site, secondary] or Neoplasm, neoplastic unknown site or unspecified .

Unspecified diagnosis codes like C79.9 are acceptable when clinical information is unknown or not available about a particular condition. Although a more specific code is preferable, unspecified codes should be used when such codes most accurately reflect what is known about a patient's condition. Specific diagnosis codes should not be used if not supported by the patient's medical record.

Approximate Synonyms

The following clinical terms are approximate synonyms or lay terms that might be used to identify the correct diagnosis code:

  • Distant metastasis present
  • Germline BRCA-mutated, HER2-negative metastatic breast cancer
  • Human epidermal growth factor 2 negative carcinoma of breast
  • 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
  • Lymphedema due to malignant infiltration
  • 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
  • Malignant tumor of unknown origin
  • Metastatic acantholytic squamous cell carcinoma
  • Metastatic adenocarcinoma
  • Metastatic adenocarcinoma of unknown origin
  • Metastatic castration-resistant prostate cancer
  • Metastatic clear cell renal cell carcinoma
  • Metastatic collecting duct carcinoma
  • Metastatic extraskeletal osteosarcoma
  • Metastatic gastroesophageal adenocarcinoma
  • Metastatic hepatocellular carcinoma
  • Metastatic human epidermal growth factor 2 positive carcinoma of breast
  • Metastatic malignant melanoma
  • Metastatic malignant melanoma
  • Metastatic malignant melanoma to skin
  • Metastatic malignant melanoma with diffuse hypermelanosis
  • Metastatic malignant neoplasm
  • Metastatic malignant neoplasm to unknown site
  • Metastatic neuroblastoma
  • Metastatic pancreatic endocrine carcinoma
  • Metastatic penile cancer
  • Metastatic renal cell carcinoma
  • Metastatic small cell carcinoma
  • Metastatic squamous cell carcinoma
  • Metastatic urothelial carcinoma
  • Oligometastatic malignant neoplasm
  • Pachymeningitis
  • Pachymeningitis due to secondary malignant neoplastic disease
  • Pathologic fracture of bone at site of metastatic neoplasm
  • 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
  • Thymic epithelial neoplasm stage finding
  • 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
  • Tumor of unknown origin

Clinical Classification

Clinical Information

  • 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.

Index to Diseases and Injuries References

The following annotation back-references for this diagnosis code are found in the injuries and diseases index. The Index to Diseases and Injuries is an alphabetical listing of medical terms, with each term mapped to one or more ICD-10-CM code(s).

Convert C79.9 to ICD-9-CM

  • ICD-9-CM Code: 198.89 - Secondary malig neo NEC
    Approximate Flag - The approximate mapping means there is not an exact match between the ICD-10 and ICD-9 codes and the mapped code is not a precise representation of the original code.

Table of Neoplasms

This code is referenced in the table of neoplasms by anatomical site. For each site there are six possible code numbers according to whether the neoplasm in question is malignant, benign, in situ, of uncertain behavior, or of unspecified nature. The description of the neoplasm will often indicate which of the six columns is appropriate.

Where such descriptors are not present, the remainder of the Index should be consulted where guidance is given to the appropriate column for each morphological (histological) variety listed. However, the guidance in the Index can be overridden if one of the descriptors mentioned above is present.

Neoplasm, neoplastic Malignant
CaInSitu Benign Uncertain
»Neoplasm, neoplastic
  »metastatic NEC [See Also: Neoplasm, by site, secondary]
»Neoplasm, neoplastic
  »unknown site or unspecified

Patient Education


Cancer begins in your cells, which are the building blocks of your body. Normally, your body forms new cells as you need them, 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. These extra cells can form a mass called a tumor. Tumors can be benign or malignant. Benign tumors aren't cancer while malignant ones are. Cells from malignant tumors can invade nearby tissues. They can also break away and spread to other parts of the body.

Cancer is not just one disease but many diseases. There are more than 100 different types of cancer. Most cancers are named for where they start. For example, lung cancer starts in the lung, and breast cancer starts in the breast. The spread of cancer from one part of the body to another is called metastasis. Symptoms and treatment depend on the cancer type and how advanced it is. Most treatment plans may include surgery, radiation and/or chemotherapy. Some may involve hormone therapy, immunotherapy or other types of biologic therapy, or stem cell transplantation.

NIH: National Cancer Institute

[Learn More in MedlinePlus]

Code History

  • FY 2024 - No Change, effective from 10/1/2023 through 9/30/2024
  • FY 2023 - No Change, effective from 10/1/2022 through 9/30/2023
  • FY 2022 - No Change, effective from 10/1/2021 through 9/30/2022
  • FY 2021 - No Change, effective from 10/1/2020 through 9/30/2021
  • FY 2020 - No Change, effective from 10/1/2019 through 9/30/2020
  • FY 2019 - No Change, effective from 10/1/2018 through 9/30/2019
  • FY 2018 - No Change, effective from 10/1/2017 through 9/30/2018
  • FY 2017 - No Change, effective from 10/1/2016 through 9/30/2017
  • FY 2016 - New Code, effective from 10/1/2015 through 9/30/2016. This was the first year ICD-10-CM was implemented into the HIPAA code set.


[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.