C48.1 vs C78.6

C48.1 (Malignant neoplasm of specified parts of peritoneum) compared with C78.6 (Secondary malignant neoplasm of retroperitoneum and peritoneum), from the official CMS tabular data. C48.1 and C78.6 name the same anatomical site (cul-de-sac) with a different neoplasm behavior. MedCoder-derived

Relationship

Informational

Neoplasm table relationship

C48.1

Malignant neoplasm of specified parts of peritoneum

↔

C78.6

Secondary malignant neoplasm of retroperitoneum and peritoneum

Same anatomical site, different neoplasm behavior.

Same site — secondary malignancy (cul-de-sac)

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. C48.1 and C78.6 name the same anatomical site (cul-de-sac) 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

	C48.1Malignant neoplasm of specified parts of peritoneum	C78.6Secondary malignant neoplasm of retroperitoneum and peritoneum
Billing status	Billable	Billable
Classification	C00-D49 — Neoplasms	C00-D49 — Neoplasms
Definition	Malignant neoplasm of specified parts of peritoneum is a billable ICD-10-CM diagnosis code (C48.1).	Secondary malignant neoplasm of retroperitoneum and peritoneum is a billable ICD-10-CM diagnosis code (C78.6).
Includes	Malignant neoplasm of cul-de-sac Malignant neoplasm of mesentery Malignant neoplasm of mesocolon Malignant neoplasm of omentum	—

Edit this comparison Check a whole claim

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