C21.1 (Malignant neoplasm of anal canal) compared with D01.3 (Carcinoma in situ of anus and anal canal), from the official CMS tabular data. C21.1 and D01.3 name the same anatomical site (anus) with a different neoplasm behavior.
Same anatomical site, different neoplasm behavior.
Same site — carcinoma in situ (anus)
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. C21.1 and D01.3 name the same anatomical site (anus) 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.
| C21.1Malignant neoplasm of anal canal | D01.3Carcinoma in situ of anus and anal canal | |
|---|---|---|
| Billing status | Billable | Billable |
| Classification | C00-D49 — Neoplasms (C00-D49) | C00-D49 — Neoplasms (C00-D49) |
| Definition | Malignant neoplasm of anal canal is a billable ICD-10-CM diagnosis code (C21.1). | Carcinoma in situ of anus and anal canal is a billable ICD-10-CM diagnosis code (D01.3). |
| Includes | Malignant neoplasm of anal sphincter | 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