C79.9 Secondary malignant neoplasm of unspecified site

The ICD-10-CM code for Secondary malignant neoplasm of unspecified site is C79.9 (FY2026). It is a billable, claim-ready diagnosis code.

Classification

Chapter

2: Neoplasms (C00-D49)

Section

C76-C80: Malignant neoplasms of ill-defined, other secondary and unspecified sites (C76-C80)

Category C79

33 codes (24 billable)

FY2026 Status

Stable since FY2024

Also Known As

ICD-10-CM Alphabetic Index entries that lead to C79.9:

• Disease, diseased › metastatic
• Metastasis, metastatic › disease

Inclusion Terms

• Metastatic cancer NOS
• Metastatic disease NOS

U.S. Hospital Utilization

• An estimated 50,615 U.S. inpatient stays in 2023 included C79.9 among the documented diagnoses.
• 460 stays listed it as the principal diagnosis.

Source: National Inpatient Sample (NIS), Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality, 2016–2023. National survey-weighted estimates.

Official Coding Guidelines

Tx of primary site (TOC entry)

a. Admission/Encounter for treatment of primary site ............................................................. 33

Tx of secondary site (TOC entry)

b. Admission/Encounter for treatment of secondary site .......................................................... 33

Source: CMS — ICD-10-CM Official Guidelines for Coding and Reporting, FY2026

References

• CMS — ICD-10-CM Official Code Set and Guidelines, FY2026
• CDC/NCHS — ICD-10-CM Files and Browser Tool
• AHRQ — HCUP National Inpatient Sample, Frequencies by Diagnosis Code (2016–2023)

Cite This Page

Reference C79.9 with the canonical source and edition:

C79.9 — Secondary malignant neoplasm of unspecified site. ICD-10 Coding Pro (ICD-10-CM FY2026). https://icd10codingpro.com/codes/C79.9

Canonical URL: https://icd10codingpro.com/codes/C79.9