2027 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 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

C45.1 is a billable ICD-10-CM diagnosis code for mesothelioma of peritoneum. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 374 through 376. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 6 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Mesothelioma.

For Medicare Advantage risk adjustment, C45.1 maps to CMS-HCC Category 19 (Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers) under the V28 model, adding a risk factor of about 1.798 for a community, non-dual, aged beneficiary in payment year 2027.

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

Medicare Risk Adjustment (HCC)Billing

C45.1 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2027.

CMS-HCC V28 Category (Payment Model)
HCC 19— Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers
Payment HCC · PY 2027 one of 68 ICD-10-CM codes in this category
Risk Adjustment Factor (RAF) Weight
+1.798
community, non-dual, aged · ranges 0.957–1.989 across segments
Hierarchy
Superseded by HCC 17 and HCC 18
a more severe related category takes the payment when both are reported
Prior Model (CMS-HCC V24)
HCC 9
V24 retired V28 pays 100% of MA risk scores since PY 2026
Other CMS Models
PACE (CMS-HCC V22): HCC 9 · ESRD (V21): HCC 9 · ESRD (V24): HCC 9
ESRD V21 weights: 0.169 dialysis, 0.604–0.975 functioning graft · ESRD V24 weights: 0.181 dialysis, 0.770–1.226 functioning graft
Part D (RxHCC)
RxHCC 22 — Prostate, Breast, Bladder, and Other Cancers and Tumors
also risk-adjusts in the Part D prescription drug model (V08)

Source: CMS Payment Year 2027 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.

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

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to C45.1: its own notes plus those printed at Chapter 2. A note printed at a category, block or chapter applies to every code under it.

Applicable To

Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.

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

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

  • other malignant neoplasm of soft tissue of peritoneum (C48.-)

Notes

General instructions on how these codes are used.

From Chapter 2 (C00-D49) Neoplasms applies to 1,730 codes
  • Functional activity
  • All neoplasms are classified in this chapter, whether they are functionally active or not. An additional code from Chapter 4 may be used, to identify functional activity associated with any neoplasm.
  • Morphology [Histology]
  • Chapter 2 classifies neoplasms primarily by site (topography), with broad groupings for behavior, malignant, in situ, benign, etc. The Table of Neoplasms should be used to identify the correct topography code. In a few cases, such as for malignant melanoma and certain neuroendocrine tumors, the morphology (histologic type) is included in the category and codes.
  • Primary malignant neoplasms overlapping site boundaries
  • A primary malignant neoplasm that overlaps two or more contiguous (next to each other) sites should be classified to the subcategory/code .8 ('overlapping lesion'), unless the combination is specifically indexed elsewhere. For multiple neoplasms of the same site that are not contiguous, such as tumors in different quadrants of the same breast, codes for each site should be assigned.
  • Malignant neoplasm of ectopic tissue
  • Malignant neoplasms of ectopic tissue are to be coded to the site mentioned, e.g., ectopic pancreatic malignant neoplasms are coded to pancreas, unspecified (C25.9).

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name C45.1, its category, or a range that includes it.

Applicable To 1

These notes mention C45.1.

  • Z85.83 Personal history of malignant neoplasm of bone and soft tissue
    Conditions classifiable to C40-C41; C45-C49 names C45-C49, which includes this code

Excludes1 3

These codes carry an Excludes1 note naming C45.1: they are not reported together with it, unless the two conditions are unrelated.

  • Block C30-C39 Malignant neoplasms of respiratory and intrathoracic organs
    mesothelioma (C45.-) names C45.-, which includes this code
  • C38 Malignant neoplasm of heart, mediastinum and pleura
    mesothelioma (C45.-) names C45.-, which includes this code
  • C48 Malignant neoplasm of retroperitoneum and peritoneum
    mesothelioma (C45.-) names C45.-, which includes this code

Excludes2 1

These codes carry an Excludes2 note naming C45.1: its condition is not part of those codes, and both may be reported when the patient has both.

  • C49 Malignant neoplasm of other connective and soft tissue
    mesothelioma (C45.-) names C45.-, which includes this code

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

Clinical ClassificationClinical

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

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

Clinical InformationClinical

  • Peritoneal Mesothelial Neoplasm

    a mesothelial neoplasm that arises from the peritoneum. it includes adenomatoid tumor, well differentiated papillary mesothelial tumor, multicystic mesothelioma, and malignant mesothelioma.

  • 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)

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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About C45.1Overview

What is the ICD-10 code for mesothelioma of peritoneum?

The ICD-10-CM code for mesothelioma of peritoneum is C45.1 (sometimes written as C451). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

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, 2026 through September 30, 2027.

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 375, 374, 376, with relative weights from 0.8925 to 2.1101 depending on complications. Higher weights mean higher Medicare reimbursement.

Is C45.1 a CC or MCC?

CMS lists C45.1 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 6 closely related codes in its exclusion list.

Can C45.1 be reported with a code from C48?

Not as a rule. The Excludes1 note on C45.1 lists "other malignant neoplasm of soft tissue of peritoneum (C48.-)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).

What HCC is C45.1?

C45.1 (mesothelioma of peritoneum) maps to CMS-HCC Category 19 (Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers), commonly written as HCC 19, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It mapped to HCC 9 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. In the Part D prescription drug model it maps to RxHCC 22.

Does C45.1 risk-adjust for Medicare Advantage payment?

Yes. When documented and reported on a Medicare Advantage encounter, C45.1 adds a risk adjustment factor of about 1.798 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.957 to 1.989 depending on the payment segment). A more severe related category (HCC 17 and HCC 18) supersedes it when both are reported. See the full factor table on the HCC 19 category page.