C21.0 (Malignant neoplasm of anus, unspecified) compared with D37.8 (Neoplasm of uncertain behavior of other specified digestive organs), from the official CMS tabular data. C21.0 and D37.8 name the same anatomical site (anus) with a different neoplasm behavior. MedCoder-derived
Same anatomical site, different neoplasm behavior.
Same site — uncertain behavior (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. C21.0 and D37.8 name the same anatomical site (anus) 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.
| C21.0Malignant neoplasm of anus, unspecified | D37.8Neoplasm of uncertain behavior of other specified digestive organs | |
|---|---|---|
| Billing status | Billable | Billable |
| Classification | C00-D49 — Neoplasms | C00-D49 — Neoplasms |
| Definition | Malignant neoplasm of anus, unspecified is a billable ICD-10-CM diagnosis code (C21.0). | Neoplasm of uncertain behavior of other specified digestive organs is a billable ICD-10-CM diagnosis code (D37.8). |
| Includes | — | Neoplasm of uncertain behavior of anal canal Neoplasm of uncertain behavior of anal sphincter Neoplasm of uncertain behavior of anus NOS Neoplasm of uncertain behavior of esophagus |
Derived from the official CMS ICD-10-CM tabular data (FY2026). Not billing advice; verify sequencing rules for the encounter. All data sources