C49.9 vs D21.9

C49.9 (Malignant neoplasm of connective and soft tissue, unspecified) compared with D21.9 (Benign neoplasm of connective and other soft tissue, unspecified), from the official CMS tabular data. C49.9 and D21.9 name the same anatomical site (aponeurosis) with a different neoplasm behavior.

Relationship

Informational

Neoplasm table relationship

C49.9

Malignant neoplasm of connective and soft tissue, unspecified

↔

D21.9

Benign neoplasm of connective and other soft tissue, unspecified

Same anatomical site, different neoplasm behavior.

Same site — benign neoplasm (aponeurosis)

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. C49.9 and D21.9 name the same anatomical site (aponeurosis) 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.

Side by side

	C49.9Malignant neoplasm of connective and soft tissue, unspecified	D21.9Benign neoplasm of connective and other soft tissue, unspecified
Billing status	Billable	Billable
Classification	C00-D49 — Neoplasms (C00-D49)	C00-D49 — Neoplasms (C00-D49)
Definition	Malignant neoplasm of connective and soft tissue, unspecified is a billable ICD-10-CM diagnosis code (C49.9).	Benign neoplasm of connective and other soft tissue, unspecified is a billable ICD-10-CM diagnosis code (D21.9).
Includes	malignant neoplasm of blood vessel malignant neoplasm of bursa malignant neoplasm of cartilage malignant neoplasm of fascia	benign neoplasm of blood vessel benign neoplasm of bursa benign neoplasm of cartilage benign neoplasm of fascia

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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