While most breast cancers originate in the breast tissue itself, there are rare cases where cancer spreads (metastasizes) from another primary site—such as the lung, ovary, or prostate—to the breast. In such cases, the ICD-10 code C79.81 is used to document secondary malignant neoplasm of the breast.
This article will guide you on how to properly use and document C79.81, highlight clinical examples, cover common pitfalls, and show how AI tools like DocScrib can streamline oncology documentation for metastatic disease.
When to Use ICD-10 Code C79.81
Use C79.81 when:
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There is a primary cancer located elsewhere (e.g., lung, colon, ovary)
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The breast is a site of metastasis
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The malignancy is not originating in breast tissue
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Imaging or pathology confirms metastatic infiltration in the breast
Do not use C79.81 for primary breast cancer (e.g., C50.911, C50.511). It is reserved only for metastasis from other sites to the breast.
Primary vs. Secondary Malignancy: Key Difference
| Primary Cancer | Code |
|---|---|
| Originates in the breast | C50.xxx (e.g., C50.411, C50.912) |
| Originates elsewhere, spreads to breast | C79.81 |
Common Primary Sites That Metastasize to the Breast
While rare, these cancers can metastasize to the breast:
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Lung cancer (C34.90)
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Ovarian cancer (C56.9)
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Melanoma (C43.9)
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Prostate cancer (C61)
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Gastric or colon cancers (C16.9 / C18.9)
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Kidney cancer (C64.9)
Clinical Documentation Elements
To justify use of C79.81, the medical record should contain:
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Primary malignancy diagnosis and location
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Imaging findings (e.g., mammogram, CT, PET-CT) showing breast lesions
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Biopsy/pathology report confirming metastatic cancer cells
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Clinical interpretation confirming the lesion is not a primary breast tumor
Example from pathology:
“Breast lesion consistent with metastatic small-cell carcinoma, morphologically similar to known lung primary.”
SOAP Note Example – C79.81
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S: “Patient with history of stage IV ovarian cancer now has a palpable right breast mass.”
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O: PET-CT shows increased uptake in right breast. Core needle biopsy confirms metastatic serous adenocarcinoma.
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A: Secondary malignant neoplasm of right breast from ovarian primary (C79.81).
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P: Refer to oncology for systemic treatment. Consider palliative radiation for breast lesion.
Additional ICD-10 Codes Often Paired With C79.81
| Clinical Element | ICD-10 Code |
|---|---|
| Primary malignancy – lung | C34.90 |
| Primary malignancy – ovary | C56.9 |
| Personal history of malignancy | Z85.xx |
| Secondary neoplasm of liver | C78.7 |
| Secondary neoplasm of bone | C79.51 |
| Encounter for chemotherapy | Z51.11 |
| Encounter for palliative care | Z51.5 |
Imaging & Diagnosis Workflow
| Modality | Purpose |
|---|---|
| PET-CT | Whole-body scan to locate secondary sites |
| Breast ultrasound | Evaluates masses, cysts, or nodules |
| CT chest/abdomen/pelvis | Evaluates spread from lung or GI origin |
| Mammogram | Rarely first-line in metastatic workup |
| Core biopsy/FNA | Confirms cancer subtype and origin |
Pathology Language to Look For
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“Findings consistent with metastatic adenocarcinoma”
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“Immunohistochemistry matches known colon primary”
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“ER/PR negative, HER2 equivocal—profile suggests non-breast origin”
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“Tumor cells express TTF-1, indicating lung origin”
Treatment Considerations
| Strategy | Clinical Focus |
|---|---|
| Systemic therapy | Chemotherapy, immunotherapy for primary tumor type |
| Hormone therapy | If ER/PR+ and originating from hormonal tissue |
| Palliative radiation | May be used for breast pain or local control |
| Surgical excision | Rarely used unless lesion causes discomfort |
| Palliative care | Z51.5 – for symptom control in advanced cases |
FAQs
Can I code C79.81 alone?
No. Always pair it with the primary malignancy code (e.g., C34.90 for lung cancer).
Is C79.81 used if a patient has a recurrence of breast cancer?
Not unless it’s metastasis from another organ to the breast. If it’s recurrence in the same breast, use the original primary code (e.g., C50.911) and document recurrence in notes.
Should I code the laterality?
C79.81 is a non-lateralized code. However, laterality can be documented in clinical notes.
Common Coding Errors to Avoid
| Error | Correction |
|---|---|
| Using C50.xxx (primary breast cancer) for metastatic cases | Use C79.81 + primary cancer code |
| Omitting documentation of primary tumor | Always include original site diagnosis (e.g., C56.9) |
| Using C79.81 for recurrent local breast cancer | Recode under the original breast cancer ICD-10 code |
How DocScrib Simplifies Oncology Coding
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✅ Extracting primary and metastatic sites from imaging/pathology reports
✅ Auto-suggesting correct secondary ICD-10 codes like C79.81
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✅ Generating oncology-focused SOAP templates and follow-up notes
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Conclusion
ICD-10 Code C79.81 should be used whenever a metastatic tumor spreads to the breast from a primary site elsewhere in the body. Accurate use of this code, combined with clear documentation of the primary malignancy, enhances care continuity, clinical decision-making, and billing accuracy.
Let DocScrib handle the documentation while you focus on the patient.