C79.9 (Secondary malignant neoplasm of unspecified site) compared with D09.9 (Carcinoma in situ, unspecified), from the official CMS tabular data. C79.9 and D09.9 name the same anatomical site (unspecified site) with a different neoplasm behavior. MedCoder-derived
Same anatomical site, different neoplasm behavior.
Same site — carcinoma in situ (unspecified site)
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. C79.9 and D09.9 name the same anatomical site (unspecified site) with a different neoplasm behavior.
From the CMS/CDC 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.
| C79.9Secondary malignant neoplasm of unspecified site | D09.9Carcinoma in situ, unspecified | |
|---|---|---|
| Billing status | Billable | Billable |
| Classification | C00-D49 — Neoplasms (C00-D49) | C00-D49 — Neoplasms (C00-D49) |
| Definition | Secondary malignant neoplasm of unspecified site is a billable ICD-10-CM diagnosis code (C79.9). | Carcinoma in situ, unspecified is a billable ICD-10-CM diagnosis code (D09.9). |
| Includes | Metastatic cancer NOS Metastatic disease NOS | Bowen's disease erythroplasia grade III intraepithelial neoplasia Queyrat's erythroplasia |
Derived from the official CMS ICD-10-CM tabular data (FY2026). Not billing advice; verify sequencing rules for the encounter. All data sources