ICD-10 C79.9
Billable / Specific HCC v28: 8 CCSecondary malignant neoplasm of unspecified site
About ICD-10-CM C79.9
ICD-10-CM code C79.9 represents Secondary malignant neoplasm of unspecified site. This is a billable/specific code in the chapter (block C79). The 2026 edition of ICD-10-CM C79.9 became effective on October 1, 2025.
Coding Tips for C79.9
Specialist guidance from the PayerReady Medical Coding Team. Specificity warnings, HCC capture rules, sequencing notes.
C79.9 is a CMS-HCC v28 risk-adjustment code (category 8). To count for the patient Risk Adjustment Factor (RAF), document the diagnosis with MEAT language each calendar year: Monitored, Evaluated, Assessed, Treated. A diagnosis on the problem list alone does not satisfy CMS RADV audit standards. Include the diagnosis in the assessment with current status and current treatment plan.
C79.9 is designated CC for MS-DRG grouping. On inpatient claims, this code can shift the DRG to the with-CC variant when documented as a present-on-admission secondary diagnosis. Hospital CDI programs flag CC opportunities during chart review. Failure to capture this code may leave 30 to 80 percent of the inpatient stay revenue unrealized.
Inclusion Terms / Approximate Synonyms
Clinical terms and conditions classified under C79.9. Per CMS ICD-10-CM Tabular 2026.
- Metastatic cancer NOS
- Metastatic disease NOS
Type 1 Excludes
Pure excludes, these codes can never be coded together with C79.9. The conditions are mutually exclusive (e.g., congenital vs acquired forms).
- carcinomatosis NOS (C80.0)
- generalized cancer NOS (C80.0)
- malignant (primary) neoplasm of unspecified site (C80.1)
Medicare Advantage HCC Impact
Capture this diagnosis annually for accurate risk adjustment. Missed HCC captures are the #1 revenue leak in Medicare Advantage risk programs.
Inpatient DRG Impact, CC
codes Secondary malignant neoplasm of unspecified site. As a Complication/Comorbidity (CC), this contributes to DRG severity adjustment when documented alongside the principal diagnosis.
Medicare LCD Coverage for C79.9
Local Coverage Determinations (LCDs) from CMS MACs that list C79.9 as a covered diagnosis.
Showing top 10 of 189 total . Click a CPT for full coverage scope.
Commercial Payer Coverage
Coverage policies from major commercial payers referencing C79.9.
5 Medicare
CPT Codes Commonly Billed with C79.9
Procedures frequently paired with this diagnosis based on PayerReady's Dx↔Px linkage data.
- C8925 CMS LCD: Billing and Coding: Transesophageal Echocardiography (TEE) CMS LCD
- C8927 CMS LCD: Billing and Coding: Transesophageal Echocardiography (TEE) CMS LCD
- C8926 CMS LCD: Billing and Coding: Transesophageal Echocardiography (TEE) CMS LCD
- 75574 CMS LCD: Billing and Coding: Coronary Computed Tomography Angiography (CCTA) CMS LCD
- 75573 CMS LCD: Billing and Coding: Coronary Computed Tomography Angiography (CCTA) CMS LCD
- 75572 CMS LCD: Billing and Coding: Coronary Computed Tomography Angiography (CCTA) CMS LCD
- 75571 CMS LCD: Billing and Coding: Coronary Computed Tomography Angiography (CCTA) CMS LCD
Convert C79.9 to ICD-9-CM
Per CMS General Equivalence Mappings (GEMs), useful for legacy data review and historical claim analysis.
| ICD-10 | ICD-9 | Mapping Flags |
|---|---|---|
| C79.9 | 19889 | 10000 |
Flags format (5 digits): Approximate · No Map · Combination · Scenario · Choice List. Source: CMS 2017 GEMs (final version).
Codes Adjacent To C79.9
Other codes in section C76-C80 (Malignant neoplasms of ill-defined, other secondary and unspecified sites).
ICD-10 C79.9, Billing FAQ
Is ICD-10 code C79.9 billable? +
Yes, C79.9 is a billable ICD-10-CM code that can appear as a primary or secondary diagnosis on claims.
What other names or terms map to C79.9? +
ICD-10 C79.9 includes: Metastatic cancer NOS; Metastatic disease NOS.
What codes are Type 1 Excludes for C79.9? +
Type 1 Excludes (never code together with C79.9): carcinomatosis NOS (C80.0); generalized cancer NOS (C80.0); malignant (primary) neoplasm of unspecified site (C80.1)
Does C79.9 affect Medicare Advantage HCC risk adjustment? +
Yes. C79.9 maps to CMS-HCC v28 category 8. Capture this diagnosis annually for accurate Medicare Advantage risk score.
Is C79.9 a CC or MCC for inpatient DRG? +
Yes, this code is designated as CC. Documenting as a secondary diagnosis on inpatient claims can shift the DRG to a higher-weighted category.
What CPT codes are commonly billed with C79.9? +
Procedures frequently paired with C79.9 include: C8925, C8927, C8926, 75574, 75573.
What ICD-9 codes does C79.9 map to? +
Per CMS GEMs, C79.9 maps to ICD-9 codes: 19889. Useful for legacy data review and historical claim analysis.
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Reviewed by the PayerReady Medical Coding Team
Verified against the CMS 2026 code set on June 1, 2026.
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