Is C79.9 a billable ICD-10-CM code?

Yes. C79.9 is a billable, specific ICD-10-CM code and is valid for submission on a claim.

Where does C79.9 sit in the tabular list?

Neoplasms (C00-D49), in the block Malignant neoplasms of ill-defined, other secondary and unspecified sites (C76-C80).

What cannot be coded together with C79.9?

C79.9 carries an Excludes1 note, which means the conditions it lists can never be coded together with it on the same encounter.

C79.9

C79.9 — Secondary malignant neoplasm of unspecified site

Billable / specific codeICD-10-CM

C79.9 is a billable, specific ICD-10-CM code for secondary malignant neoplasm of unspecified site. It is valid for submission on a claim.

Excludes1 — never code together

These conditions cannot occur together. Billing both on the same encounter is a denial.

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

Inclusion terms

Alternative wordings a physician may use in the chart for this same code.

Metastatic cancer NOS
Metastatic disease NOS

Other codes that can never be billed with C79.9

These codes carry an Excludes1 note pointing at C79.9. The conflict binds both ways, but ICD-10-CM only writes it down on one side — so you would not find this by reading C79.9 alone.

C80.1Malignant (primary) neoplasm, unspecified

Risk adjustment

C79.9 risk-adjusts. Under the CMS-HCC V28 model it maps to this category:

HCC 18 Cancer Metastatic to Bone, Other and Unspecified Metastatic Cancer; Acute Leukemia Except Myeloid2.341 RAF

Coefficient shown for the Community Non-dual Aged segment. A higher HCC in the same hierarchy will suppress this one, so capturing it does not always add score.

Medicare coverage

C79.9 is named in 23 Medicare coverage policies — 23 listing it as supporting medical necessity. Which of them applies to you depends on your Medicare contractor, and coverage genuinely differs by state.

A52479Oral Anticancer Drugs - Policy Article
A52480Oral Antiemetic Drugs (Replacement for Intravenous Antiemetics) - Policy Article
A52868Billing and Coding: Transesophageal Echocardiography (TEE)
A53101Billing and Coding: MolDX: bioTheranostics Cancer TYPE ID® Update

How C79.9 is indexed

Coders do not find codes by browsing the tabular list — they look them up in the alphabetic index, under the word the physician wrote. These are the index entries that lead here, so you can see which chart wordings map to C79.9.

Disease, diseased›metastatic
Metastasis, metastatic›disease

Related codes at this level

Codes that share C79. If C79.9 is not quite right, the correct code is usually one of these.

Questions about C79.9

Is C79.9 a billable ICD-10-CM code?: Yes. C79.9 is a billable, specific ICD-10-CM code and is valid for submission on a claim.
Where does C79.9 sit in the tabular list?: Neoplasms (C00-D49), in the block Malignant neoplasms of ill-defined, other secondary and unspecified sites (C76-C80).
What cannot be coded together with C79.9?: C79.9 carries an Excludes1 note, which means the conditions it lists can never be coded together with it on the same encounter.