C45.1 Mesothelioma of peritoneum

The ICD-10-CM code for Mesothelioma of peritoneum is C45.1 (FY2026). It is a billable, claim-ready diagnosis code.

Classification

Chapter

2: Neoplasms (C00-D49)

Section

C45-C49: Malignant neoplasms of mesothelial and soft tissue (C45-C49)

Category C45

6 codes (5 billable)

FY2026 Status

Stable since FY2024

Also Known As

ICD-10-CM Alphabetic Index entries that lead to C45.1:

• Mesothelioma (malignant) › site classification › mesentery
• Mesothelioma (malignant) › site classification › peritoneum
• Mesothelioma (malignant) › site classification › mesocolon
• Mesothelioma (malignant) › site classification › omentum

Inclusion Terms

• Mesothelioma of cul-de-sac
• Mesothelioma of mesentery
• Mesothelioma of mesocolon
• Mesothelioma of omentum
• Mesothelioma of peritoneum (parietal) (pelvic)

U.S. Hospital Utilization

• An estimated 1,170 U.S. inpatient stays in 2023 included C45.1 among the documented diagnoses.
• 385 stays listed it as the principal diagnosis.

Source: National Inpatient Sample (NIS), Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality, 2016–2023. National survey-weighted estimates.

Official Coding Guidelines

Tx of primary site (TOC entry)

a. Admission/Encounter for treatment of primary site ............................................................. 33

Tx of secondary site (TOC entry)

b. Admission/Encounter for treatment of secondary site .......................................................... 33

Source: CMS — ICD-10-CM Official Guidelines for Coding and Reporting, FY2026

References

• CMS — ICD-10-CM Official Code Set and Guidelines, FY2026
• CDC/NCHS — ICD-10-CM Files and Browser Tool
• AHRQ — HCUP National Inpatient Sample, Frequencies by Diagnosis Code (2016–2023)