C50.9 (Malignant neoplasm of breast of unspecified site) compared with C79.81 (Secondary malignant neoplasm of breast), from the official CMS tabular data. C50.9 and C79.81 name the same anatomical site (breast) with a different neoplasm behavior.
Same anatomical site, different neoplasm behavior.
Same site — secondary malignancy (breast)
The behavior documented for the site — malignant primary, secondary, carcinoma in situ, benign, uncertain or unspecified — decides which column of the neoplasm table, and therefore which code, applies.
Source: CMS Table of Neoplasms
Same site, different neoplasm behavior. C50.9 and C79.81 name the same anatomical site (breast) with a different neoplasm behavior.
From the CMS Table of Neoplasms: the behavior documented for that site — malignant primary, secondary, carcinoma in situ, benign, uncertain or unspecified — decides which column, and therefore which code, applies.
| C50.9Malignant neoplasm of breast of unspecified site | C79.81Secondary malignant neoplasm of breast | |
|---|---|---|
| Billing status | Non-billable header | Billable |
| Classification | C00-D49 — Neoplasms (C00-D49) | C00-D49 — Neoplasms (C00-D49) |
| Definition | Malignant neoplasm of breast of unspecified site is a non-billable ICD-10-CM category code (C50.9). | Secondary malignant neoplasm of breast is a billable ICD-10-CM diagnosis code (C79.81). |
| Includes | connective tissue of breast Paget's disease of breast Paget's disease of nipple | — |
| Use additional code | code to identify estrogen, and other hormones and factors receptor status (Z17.-) | — |
Derived from the official CMS ICD-10-CM tabular data (FY2026). Not billing advice; verify sequencing rules for the encounter. All data sources