C79.9 — Secondary malignant neoplasm of unspecified site

BillableUnspecifiedCC

Is C79.9 billable?

Yes, but C79.9 is an unspecified code. C79.9 is a valid, billable ICD-10-CM code for encounters from October 1, 2026 through September 30, 2027. However, C79.9 is an unspecified or catch-all code. Payers apply additional scrutiny to unspecified codes and many deny them when the medical record supports a more specific option, so check the documentation before selecting C79.9 — the more specific alternatives are listed below.

More specific alternatives

C79.9 at a glance

Code	C79.9
Description	Secondary malignant neoplasm of unspecified site
Billable	Yes
Code set	ICD-10-CM FY2027
Valid for encounters	October 1, 2026 – September 30, 2027

Which MS-DRGs does C79.9 group to?

C79.9 sits in MDC 17 and helps define the logic of 3 MS-DRGs (version 44, FY2027). Which one a stay actually groups to also depends on procedures and secondary diagnoses.

826Myeloproliferative Disorders or Poorly Differentiated Neoplasms with Major O.R. Procedures with MCCsurgical
827Myeloproliferative Disorders or Poorly Differentiated Neoplasms with Major O.R. Procedures with CCsurgical
828Myeloproliferative Disorders or Poorly Differentiated Neoplasms with Major O.R. Procedures without CC/MCCsurgical

As a secondary diagnosis, C79.9 is a complication or comorbidity (CC), which can move a stay into a higher-paying DRG.

How is C79.9 listed in the Alphabetic Index?

These are the routes through the Alphabetic Index that lead to C79.9. They show the wording a clinician may have documented, which often differs from the Tabular description.

Disease, diseased › metastatic
Metastasis, metastatic › disease

Excludes1 — never code together

The conditions below can never be reported together with C79.9 on the same claim. An Excludes1 note means the two conditions cannot occur in the same patient, so reporting both is a coding error.

carcinomatosis NOS (C80.0)
generalized cancer NOS (C80.0)
malignant (primary) neoplasm of unspecified site (C80.1)

Inclusion terms

Alternative wording in documentation that is classified to C79.9.

Metastatic cancer NOS
Metastatic disease NOS

Excludes1 — never code together — inherited from C79

The conditions below can never be reported together with C79.9 on the same claim. An Excludes1 note means the two conditions cannot occur in the same patient, so reporting both is a coding error.

secondary carcinoid tumors (C7B.-)
secondary neuroendocrine tumors (C7B.-)

How long has C79.9 existed?

C79.9 has been in ICD-10-CM since at least FY2016, the earliest fiscal year on record here.

Derived from the official order files for FY2016–FY2026. FY2017 and FY2020 publish no order file, so those years are not covered.

Which codes are confused with C79.9?

ICD-10-CM declares these codes mutually exclusive with C79.9 — exactly one of each pair can be correct for a given encounter.