C21.8 vs D49.0

C21.8 (Malignant neoplasm of overlapping sites of rectum, anus and anal canal) compared with D49.0 (Neoplasm of unspecified behavior of digestive system), from the official CMS tabular data. C21.8 and D49.0 name the same anatomical site (anorectum) with a different neoplasm behavior. MedCoder-derived

Relationship

Informational

Neoplasm table relationship

C21.8

Malignant neoplasm of overlapping sites of rectum, anus and anal canal

↔

D49.0

Neoplasm of unspecified behavior of digestive system

Same anatomical site, different neoplasm behavior.

Same site — unspecified behavior (anorectum)

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

Can these codes be reported together?

Same site, different neoplasm behavior. C21.8 and D49.0 name the same anatomical site (anorectum) 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.

Side by side

	C21.8Malignant neoplasm of overlapping sites of rectum, anus and anal canal	D49.0Neoplasm of unspecified behavior of digestive system
Billing status	Billable	Billable
Classification	C00-D49 — Neoplasms	C00-D49 — Neoplasms
Definition	Malignant neoplasm of overlapping sites of rectum, anus and anal canal is a billable ICD-10-CM diagnosis code (C21.8).	Neoplasm of unspecified behavior of digestive system is a billable ICD-10-CM diagnosis code (D49.0).
Includes	Malignant neoplasm of anorectal junction Malignant neoplasm of anorectum Primary malignant neoplasm of two or more contiguous sites of rectum, anus and anal canal	'growth' NOS neoplasm NOS new growth NOS tumor NOS

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Derived from the official CMS ICD-10-CM tabular data (FY2026). Not billing advice; verify sequencing rules for the encounter. All data sources