ICD-10 Code C79.81 – Secondary malignant neoplasm of breast (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C79.81 – Secondary malignant neoplasm of breast
What it is
C79.81 identifies metastatic cancer that has spread to the breast from another primary site. Use this code when the breast lesion is documented as secondary, not as a new primary breast cancer.
Clinical signs
Clinical features vary; refer to documentation. Findings may include a breast mass, skin or nipple changes, or imaging and pathology showing metastatic disease rather than a primary breast tumor.
When to use this code
Use C79.81 when the provider documents secondary malignant involvement of the breast, such as metastasis from lung, melanoma, ovarian, or other primary cancers. Code it when the breast is a site of spread and the record supports metastatic disease. If the primary source is not stated, check documentation.
Do not use for
Do not use this code for primary breast cancer or benign breast masses. It is also incorrect when the breast finding is suspected but not confirmed as metastatic disease.
Coding tip
Always code the known primary malignancy first, when documented, and add C79.81 only for confirmed secondary breast involvement.