C06.9 (Malignant neoplasm of mouth, unspecified) compared with C79.83 (Secondary malignant neoplasm of oral cavity), from the official CMS tabular data. C06.9 and C79.83 name the same anatomical site (oral) with a different neoplasm behavior. MedCoder-derived
Same anatomical site, different neoplasm behavior.
Same site — secondary malignancy (oral)
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. C06.9 and C79.83 name the same anatomical site (oral) 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.
| C06.9Malignant neoplasm of mouth, unspecified | C79.83Secondary malignant neoplasm of oral cavity | |
|---|---|---|
| Billing status | Billable | Billable |
| Classification | C00-D49 — Neoplasms (C00-D49) | C00-D49 — Neoplasms (C00-D49) |
| Definition | Malignant neoplasm of mouth, unspecified is a billable ICD-10-CM diagnosis code (C06.9). | — |
| Includes | Malignant neoplasm of minor salivary gland, unspecified site Malignant neoplasm of oral cavity NOS | — |
| Use additional code | code to identify: alcohol abuse and dependence (F10.-) history of tobacco dependence (Z87.891) | — |
Derived from the official CMS ICD-10-CM tabular data (FY2026). Not billing advice; verify sequencing rules for the encounter. All data sources