2026 ICD-10-CM Diagnosis Code C45.1Mesothelioma of peritoneum

ICD-10-CM Codes›C00–D49›C45-C49›C45

ICD-10-CM C45.1
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

C45.1 is a billable ICD-10-CM diagnosis code for mesothelioma of peritoneum. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 374 through 376. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Mesothelioma.

Code Identity

ICD-10-CM Code
C45.1
Billable Status
Yes — Valid for Submission
Code Describes
Mesothelioma of peritoneum
Short Description
Mesothelioma of peritoneum
Same as the full description in the CMS dataset.
Parent Code
C45
Mesothelioma

Code Classification

ChapterC00–D49Neoplasms
SectionC45-C49Malignant neoplasms of mesothelial and soft tissue
CategoryC45Mesothelioma
This CodeC45.1Mesothelioma of peritoneum

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Malignant mesothelioma of mesentery
  • Malignant mesothelioma of mesocolon
  • Malignant mesothelioma of omentum
  • Malignant mesothelioma of parietal peritoneum
  • Malignant mesothelioma of pelvic peritoneum
  • Malignant mesothelioma of peritoneum
  • Malignant neoplasm of mesocolon
  • Malignant neoplasm of omentum
  • Malignant neoplasm of peritoneum and retroperitoneum
  • Neoplasm of omentum
  • Neoplasm of peritoneum and retroperitoneum
  • Neoplasm of the mesocolon
  • Overlapping malignant neoplasm of retroperitoneum and peritoneum
  • Primary malignant mesothelioma of mesentery
  • Primary malignant mesothelioma of omentum
  • Primary malignant mesothelioma of parietal peritoneum
  • Primary malignant mesothelioma of pelvic peritoneum
  • Primary malignant mesothelioma of peritoneum
  • Primary malignant neoplasm of omentum
  • Primary malignant neoplasm of parietal peritoneum
  • Primary malignant neoplasm of pelvic peritoneum
  • Primary malignant neoplasm of the mesentery
  • Primary mesothelioma of overlapping sites of retroperitoneum, peritoneum and omentum

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

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

Type 1 Excludes

  • other malignant neoplasm of soft tissue of peritoneum C48

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

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

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR NEO067
Mesothelioma
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Mesothelioma

    a tumor derived from mesothelial tissue (peritoneum, pleura, pericardium). it appears as broad sheets of cells, with some regions containing spindle-shaped, sarcoma-like cells and other regions showing adenomatous patterns. pleural mesotheliomas have been linked to exposure to asbestos. (dorland, 27th ed)

  • Mesothelioma, Cystic

    a peritoneal mesothelioma affecting mainly young females and producing cysts of variable size and number lined by a single layer of benign mesothelial cells. the disease follows a benign course and is compatible with a normal life expectancy, requiring occasionally partial excision or decompression for relief of pain or other symptoms. malignant potential is exceptional. (from holland et al., cancer medicine, 3d ed, p1345)

  • Mesothelioma, Malignant

    a type of mesothelioma with a tendency to metastasize. most tumors originate from either the pleura or peritoneum, tumors may also originate in the pericardium or testicular tissue. it is associated with asbestos exposure. somatic mutations identified in wt1, bcl10, cdkn2a, nf2, and bap1 genes are associated with the malignancy. omim: 156240.

  • Solitary Fibrous Tumor, Pleural

    a rare neoplasm, usually benign, derived from mesenchymal fibroblasts located in the submesothelial lining of the pleura. it spite of its various synonyms, it has no features of mesothelial cells and is not related to malignant mesothelioma or asbestos exposure.

Patient EducationClinical

Mesothelioma

The tissue that lines your lungs, stomach, heart, and other organs is called mesothelium. Mesothelioma, also known as malignant mesothelioma, is cancer of that tissue. It usually starts in the lungs, but can also start in the abdomen or other organs.

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert C45.1 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
158.8 Mal neo peritoneum NEC
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About C45.1Overview

Is C45.1 (Mesothelioma) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report mesothelioma of peritoneum on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does C45.1 group to?

When mesothelioma of peritoneum is the principal diagnosis on an inpatient stay, it groups to MS-DRG 374, 375, 376, with relative weights from 0.9243 to 2.1387 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of C45.1?

Under the General Equivalence Mappings, mesothelioma of peritoneum converts to ICD-9-CM 158.8 (mal neo peritoneum NEC). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.