2027 ICD-10-CM Diagnosis Code C45.9Mesothelioma, unspecified
ICD-10-CM Codes›C00–D49›C45-C49›C45
- Billable — Valid for Submission
- Risk Adjusts — HCC 19
- Chronic Condition
C45.9 is a billable ICD-10-CM diagnosis code for mesothelioma, unspecified. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 826 through 830, 843 through 845. Coders also document this condition as malignant neoplasm of mesothelium. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Mesothelioma.
For Medicare Advantage risk adjustment, C45.9 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
Code Classification
Medicare Risk Adjustment (HCC)Billing
C45.9 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.
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 neoplasm of mesothelium
- Mesothelioma
- Neoplasm of mesothelial tissue
- Primary malignant mesothelioma
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to C45.9: its own notes plus those printed at Chapter 2. A note printed at a category, block or chapter applies to every code under it.
Notes
General instructions on how these codes are used.
- 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 C45.9, its category, or a range that includes it.
Applicable To 1
These notes mention C45.9.
- Z85.83 Personal history of malignant neoplasm of bone and soft tissue
Excludes1 3
These codes carry an Excludes1 note naming C45.9: they are not reported together with it, unless the two conditions are unrelated.
- Block C30-C39 Malignant neoplasms of respiratory and intrathoracic organsmesothelioma (C45.-) names C45.-, which includes this code
- C38 Malignant neoplasm of heart, mediastinum and pleuramesothelioma (C45.-) names C45.-, which includes this code
- C48 Malignant neoplasm of retroperitoneum and peritoneummesothelioma (C45.-) names C45.-, which includes this code
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
Mesothelioma (malignant) C45.9
biphasic C45.9
epithelioid C45.9
fibrous C45.9
unspecified C45.9
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
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)
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 C45.9 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About C45.9Overview
What is the ICD-10 code for mesothelioma, unspecified?
The ICD-10-CM code for mesothelioma, unspecified is C45.9 (sometimes written as C459). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is C45.9 (Mesothelioma) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report mesothelioma, unspecified on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does C45.9 group to?
When mesothelioma, unspecified is the principal diagnosis on an inpatient stay, it groups to MS-DRG 844, 827, 829, 843, 828, 826, 830, 845, with relative weights from 0.8443 to 4.7560 depending on complications. Higher weights mean higher Medicare reimbursement.
What is the ICD-9 equivalent of C45.9?
Under the General Equivalence Mappings, mesothelioma, unspecified converts to ICD-9-CM 199.1 (malignant neoplasm NOS). The mapping is approximate, so confirm the match fits the documentation.
What HCC is C45.9?
C45.9 (mesothelioma, unspecified) 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 C45.9 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, C45.9 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.
