What Does ICD-10 Code C79.89 Mean?
ICD-10 code C79.89 identifies a secondary malignant neoplasm — meaning metastatic cancer — located at a specified anatomical site that is not individually enumerated elsewhere in the C79 category. This is a valid, billable diagnosis code under the ICD-10-CM classification system and applies exclusively to patients with a documented history or active primary malignancy that has spread to a secondary location.
Key attributes of this code:
- Billable and valid for all current ICD-10-CM fiscal years
- Applies to metastatic disease only — not primary tumors
- Used when the secondary site is specified in documentation but does not match a more precise C79 subcategory
- Requires identification and coding of the primary malignancy whenever known
What Conditions and Diagnoses Does C79.89 Cover?
C79.89 captures metastatic disease affecting sites for which ICD-10-CM does not assign a dedicated secondary malignancy code. It is the appropriate code when the provider documents a specific secondary site that falls outside the more commonly enumerated locations such as lung, liver, bone, or brain.
Clinical presentations and scenarios this code covers include:
- Metastatic carcinoma to the adrenal gland (when not otherwise specified elsewhere)
- Secondary malignant involvement of the spleen, pancreas, small intestine, or other visceral organs without a more specific code
- Metastatic spread to soft tissue sites documented by name but not individually classified in C79
- Secondary neoplasm of the skin at a specified site when confirmed as metastatic
What Does C79.89 Specifically Exclude?
The following conditions and site-specific metastases are excluded from C79.89 and should be coded elsewhere:
- Secondary malignant neoplasm of the lung — use C78.00–C78.02
- Secondary malignant neoplasm of the liver — use C78.7
- Secondary malignant neoplasm of bone and bone marrow — use C79.51 or C79.52
- Secondary malignant neoplasm of the brain and cerebral meninges — use C79.31 or C79.32
- Secondary malignant neoplasm of the lymph nodes — use C77 series
- Secondary malignant neoplasm of the bladder, kidney, or urinary organs — use C79.10–C79.19
When Is C79.89 the Right Code to Use?
C79.89 is the correct selection only after ruling out more specific secondary malignancy codes. In practice, coders frequently encounter scenarios where providers document a secondary site by name without realizing that a more specific C79 subcategory exists — making code review against the full C79 category a mandatory step.
Follow this workflow to confirm correct code selection:
- Confirm the diagnosis is metastatic — the provider must document that the neoplasm at the specified site originated from a primary malignancy elsewhere
- Identify the secondary site explicitly named in clinical documentation
- Search the ICD-10-CM tabular list under the full C79 category to determine whether a dedicated code exists for that site
- If no dedicated code exists and the site is specified, assign C79.89
- Identify and code the primary malignancy using the appropriate C00–C76 or C80 code
- Sequence according to the reason for the encounter — the primary or secondary site may lead depending on context
How Does C79.89 Differ From C80.0 and C79.9?
| Code | Description | Key Distinction |
|---|---|---|
| C79.89 | Secondary malignant neoplasm, other specified sites | Secondary site is documented and specified; no dedicated C79 subcategory exists |
| C79.9 | Secondary malignant neoplasm, unspecified site | Secondary site is not documented or cannot be determined |
| C80.0 | Disseminated malignant neoplasm, unspecified | Widespread metastasis with no single secondary site identified; primary unknown or unspecified |
| C78.7 | Secondary malignant neoplasm of liver | Secondary liver involvement — must NOT use C79.89 |
What Documentation Is Required to Support C79.89?
Inadequate documentation is the leading driver of claim denials and audit findings for secondary malignancy codes. Payers expect explicit confirmation of both the metastatic nature of the disease and the specific site affected.
What Must the Provider Document in the Clinical Notes?
- An explicit statement that the neoplasm at the named site is metastatic or secondary in origin
- Identification of the primary malignancy site, histology, or prior cancer history
- The specific anatomical location of the secondary neoplasm — generic language such as “spread” or “mets” without a named site is insufficient
- Clinical rationale for the diagnosis — imaging findings, biopsy results, or physician confirmation
- Current treatment status of the primary malignancy if applicable to the encounter
Which Diagnostic or Lab Results Support This Code?
Supporting evidence that should appear in the medical record includes:
- Pathology or biopsy reports confirming malignant cells consistent with metastatic origin
- CT, MRI, or PET scan reports identifying the secondary site
- Oncology consultation notes referencing metastatic disease at the documented location
- Tumor markers or molecular testing results corroborating secondary involvement
What Is the Documentation Standard for Inpatient vs. Outpatient Settings?
| Setting | Documentation Standard |
|---|---|
| Inpatient | Attending physician may query to confirm or clarify metastatic nature; diagnosis code specificity must reflect the final documented conclusion per ICD-10-CM Official Coding Guidelines Section II |
| Outpatient | Coder assigns based solely on documented provider diagnosis; no assumed conditions; secondary site must be explicitly named in the assessment or impression |
How Does C79.89 Affect Medical Billing and Claims?
Secondary malignancy codes carry significant revenue cycle compliance implications because payers scrutinize them for medical necessity and appropriate primary code pairing. C79.89 is frequently submitted alongside active oncology management claims and must be supported by clinical evidence of ongoing metastatic disease.
Payer and billing considerations include:
- Medicare and commercial payers require documentation of medical necessity linking the secondary diagnosis to the services billed
- C79.89 alone does not justify chemotherapy, radiation, or surgical claims — the specific CPT codes must reflect treatment targeting the documented site
- Claims submitted without a corresponding primary malignancy code (when the primary is known) are at high risk for denial or downcoding
- Hospice and palliative care claims frequently include C79.89 and require alignment with payer-specific hospice billing rules
What CPT or Procedure Codes Are Commonly Billed With C79.89?
| CPT Code | Description | Typical Pairing Context |
|---|---|---|
| 77300–77336 | Radiation therapy planning and dosimetry | Radiation targeting a specified secondary site |
| 96401–96417 | Chemotherapy administration | Systemic or site-directed chemotherapy for metastatic disease |
| 70553 | MRI brain with and without contrast | Imaging to evaluate intracranial secondary involvement |
| 74177–74178 | CT abdomen/pelvis | Staging or monitoring of abdominal metastatic sites |
| 38221 | Bone marrow biopsy | When bone or marrow involvement accompanies other secondary sites |
Are There Any Prior Authorization or Coverage Restrictions?
- Most commercial payers require prior authorization for advanced imaging and chemotherapy infusions when billed with secondary malignancy diagnoses
- Medicare Advantage plans may apply local coverage determinations (LCDs) that require documentation of active treatment intent versus surveillance
- Some payers apply site-of-service restrictions limiting infusion services to specific facility types when metastatic disease is the primary diagnosis
What Coding Errors Should You Avoid With C79.89?
Auditors commonly flag secondary malignancy coding as one of the higher-risk areas in oncology billing, particularly when coders default to unspecified codes rather than pursuing clinical clarification.
The most frequent errors associated with C79.89, ranked by audit risk:
- Using C79.89 when a more specific C79 subcategory exists for the documented site — always check the full tabular before defaulting to this code
- Omitting the primary malignancy code when the primary site is known and documented
- Assigning C79.9 (unspecified site) when clinical documentation actually names a specific secondary location
- Treating C79.89 as a standalone principal diagnosis without sequencing context
- Applying this code to primary tumors — C79.89 is exclusively for secondary or metastatic disease
- Coding from a lab or imaging report without confirmed physician documentation of the metastatic diagnosis
What Do Auditors Look for When Reviewing Claims With C79.89?
- Whether a more specific secondary malignancy code should have been assigned
- Presence of a corresponding primary malignancy code and its accuracy
- Alignment between the billed procedure codes and the documented secondary site
- Evidence in the medical record supporting the metastatic designation (pathology, imaging, oncology notes)
- Correct sequencing based on the reason for the encounter
How Does C79.89 Relate to Other ICD-10 Codes?
Understanding C79.89’s position within the broader malignancy coding framework is essential for accurate coding audit preparation and clean claim submission.
| Related Code | Relationship Type | Key Distinction |
|---|---|---|
| C79.9 | Alternative — less specific | Use when secondary site is not documented or identifiable |
| C80.0 | Alternative — disseminated | Use for widespread metastasis, no single site identified |
| C77.0–C77.9 | Separate category | Secondary malignancy of lymph nodes — never use C79.89 for lymph node mets |
| C78.00–C78.89 | Separate category | Secondary malignancy of respiratory and digestive organs |
| Z85.xxx | History code | Use when the primary malignancy has been excised or completed treatment |
| C80.1 | Primary unknown | Use when no primary site can be determined; pair with C79.89 for the secondary site |
What Is the Correct Code Sequencing When C79.89 Appears With Other Diagnoses?
- When the patient is receiving treatment directed at the secondary site, sequence C79.89 as the principal or first-listed diagnosis
- When the patient is receiving treatment directed at the primary malignancy, sequence the primary malignancy code first and C79.89 as an additional diagnosis
- When the primary malignancy is unknown, use C80.1 followed by C79.89
- In hospice or palliative settings, follow the specific sequencing guidance in the ICD-10-CM Official Coding Guidelines Section I.C.2 for neoplasm coding
Real-World Coding Scenario — How C79.89 Is Applied in Practice
A 67-year-old male with a documented history of prostate cancer (C61) presents to his oncologist for evaluation of newly identified metastatic disease to the spleen, confirmed on CT imaging and corroborated by biopsy demonstrating cells consistent with prostatic origin. The visit is focused on evaluating and planning treatment for the splenic metastasis.
Correct Code Application
- C79.89 — Secondary malignant neoplasm of other specified sites (spleen is the documented secondary site; no dedicated C79 subcategory exists for splenic metastasis)
- C61 — Malignant neoplasm of prostate (known primary, still active)
- Sequencing: C79.89 leads because the encounter is focused on the secondary site
Common Mistake in This Scenario
- Assigning C79.9 (unspecified secondary site) because the coder did not recognize that spleen qualifies as a “specified” site under C79.89 — this results in a less specific code and potential audit flag
- Omitting C61 entirely, leaving the claim without a primary malignancy code and triggering payer denial for incomplete oncology documentation
Frequently Asked Questions About ICD-10 Code C79.89
Is ICD-10 Code C79.89 Valid for Use in the Current Fiscal Year?
C79.89 is a valid, billable ICD-10-CM diagnosis code with no recent changes to its description or validity status as of the most current fiscal year release. Coders should verify annually against the ICD-10-CM tabular updates published by CMS to confirm continued validity before large-scale claims submission.
What Is the Difference Between C79.89 and C79.9?
C79.89 is assigned when the secondary malignancy site is explicitly named in provider documentation but does not have its own dedicated C79 subcategory. C79.9 applies only when the secondary site is entirely unspecified or undocumented — coders should always query the provider or review imaging reports before defaulting to the unspecified option.
Do I Always Need to Code the Primary Malignancy Alongside C79.89?
When the primary malignancy is known and documented, it must be coded alongside C79.89 — omitting the primary code is a recognized audit vulnerability and a frequent cause of oncology claim denials. If the primary site cannot be determined, C80.1 (malignant neoplasm without specification of site) serves as the companion code.
Can C79.89 Be Used as a Principal Diagnosis?
C79.89 can be sequenced as the principal diagnosis when the admission or encounter is directed specifically at evaluation or treatment of the secondary malignancy at the documented site. The ICD-10-CM Official Coding Guidelines Section I.C.2 outlines neoplasm sequencing rules in detail and should be the definitive reference for complex oncology encounters.
What Is the Difference Between C79.89 and C80.0?
C79.89 identifies metastatic disease at a named, specific secondary site. C80.0 reflects disseminated malignancy where cancer has spread broadly without identification of a single predominant secondary location — typically documented with language such as “widely metastatic” or “carcinomatosis.” These codes are not interchangeable.
Is C79.89 Covered by Medicare for Chemotherapy Claims?
Medicare covers chemotherapy and related services for patients with active secondary malignancies when medical necessity is established through supporting clinical documentation. C79.89 must be accompanied by appropriate procedure codes, an active primary malignancy code, and documentation demonstrating that treatment is directed at the coded diagnosis — coverage is not automatic based on the diagnosis code alone.
What Should I Do If the Provider Documents “Mets” Without Naming the Site?
Documentation using vague terms like “mets” or “spread” without identifying a specific secondary site does not support C79.89. In that scenario, a query to the treating provider is warranted to clarify the exact location of metastatic involvement. If clarification is not obtainable, C79.9 would be the technically appropriate assignment, though this represents a documentation deficiency that should be flagged for medical billing documentation requirements improvement.
Key Takeaways
- C79.89 is a secondary malignancy code — it applies exclusively to metastatic cancer at a specified site not covered by a more precise C79 subcategory
- Always check the complete C79 tabular category before assigning C79.89 — a more specific code may exist for the documented site
- The secondary site must be explicitly named in provider documentation; vague metastasis language defaults to C79.9
- A corresponding primary malignancy code must accompany C79.89 whenever the primary site is known
- Sequencing depends on the focus of the encounter — secondary site treatment puts C79.89 first; primary site treatment sequences the primary first
- Claims without both primary and secondary codes are among the most commonly denied oncology submissions
- Annual verification against the current ICD-10-CM release is necessary to confirm code validity and catch any tabular revisions
For deeper sequencing guidance on neoplasm coding, the ICD-10-CM Official Coding Guidelines Section I.C.2 remains the authoritative source. The CMS ICD-10 code lookup tool at cms.gov provides the official tabular list for confirming code status and any year-over-year changes.