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C45.9 ICD-10-CM Code: Mesothelioma, unspecified

Billing Status: YES. This is a valid, specific, and billable ICD-10-CM reference.

Coding at a Glance

Risk adjustment
CMS-HCC V28: 1 category · CMS-HCC V22 category 9 · RxHCC V08 category 22

Inpatient Payment Groups (MS-DRG)

Potential MS-DRG participation — not a DRG assignment.

MS-DRGs this diagnosis helps define, as principal or secondary, per the CMS ICD-10-CM/PCS MS-DRG Definitions Manual v44, Appendix B.

  • MS-DRG 826 — MYELOPROLIFERATIVE DISORDERS OR POORLY DIFFERENTIATED NEOPLASMS WITH MAJOR O.R. PROCEDURES WITH MCC (MDC 17)
  • MS-DRG 827 — MYELOPROLIFERATIVE DISORDERS OR POORLY DIFFERENTIATED NEOPLASMS WITH MAJOR O.R. PROCEDURES WITH CC (MDC 17)
  • MS-DRG 828 — MYELOPROLIFERATIVE DISORDERS OR POORLY DIFFERENTIATED NEOPLASMS WITH MAJOR O.R. PROCEDURES WITHOUT CC/MCC (MDC 17)
  • MS-DRG 829 — MYELOPROLIFERATIVE DISORDERS OR POORLY DIFFERENTIATED NEOPLASMS WITH OTHER PROCEDURES WITH CC/MCC (MDC 17)
  • MS-DRG 830 — MYELOPROLIFERATIVE DISORDERS OR POORLY DIFFERENTIATED NEOPLASMS WITH OTHER PROCEDURES WITHOUT CC/MCC (MDC 17)
  • MS-DRG 843 — OTHER MYELOPROLIFERATIVE DISORDERS OR POORLY DIFFERENTIATED NEOPLASTIC DIAGNOSES WITH MCC (MDC 17)
  • MS-DRG 844 — OTHER MYELOPROLIFERATIVE DISORDERS OR POORLY DIFFERENTIATED NEOPLASTIC DIAGNOSES WITH CC (MDC 17)
  • MS-DRG 845 — OTHER MYELOPROLIFERATIVE DISORDERS OR POORLY DIFFERENTIATED NEOPLASTIC DIAGNOSES WITHOUT CC/MCC (MDC 17)

A diagnosis appearing in a group's logic does not by itself determine the DRG assigned to a stay; the grouper uses the full claim.

Risk Adjustment (CMS-HCC)

Payment categories this diagnosis maps to under CMS-HCC V28, payment year 2026.

  • HCC 19 — Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers (supersedes HCC 20, HCC 21, HCC 22, HCC 23)

Other models: CMS-HCC V22 HCC 9 · RxHCC V08 HCC 22

Risk scores depend on the enrollee's full accepted diagnosis set and segment; a category mapping alone does not determine payment.

Coder workflow for C45.9

MedCoder structured workflow — derived from this code’s own official record

Before you code C45.9

  1. Unspecified does not mean incorrect. When the record gives no greater specificity, C45.9 may be the appropriate code. Check the record for detail that supports a more specific sibling. An unspecified code is for records that do not provide the detail a more specific code needs; a query, not an assumption, is the route to specificity (Guidelines I.A.9.b, I.B.18).

    ReviewC45.0, C45.1, C45.2, C45.7

    See the relationships section · Guide: Other vs unspecified (NEC vs NOS) →

  2. Confirm the documented site and behavior (this code’s block classifies malignant neoplasms), whether the site is primary or secondary, and whether the malignancy is current or a personal history: a previously excised malignancy with no further treatment and no evidence of disease is history, not current disease. Verify the site against the Table of Neoplasms. Neoplasm chapter guidelines (Guidelines I.C.2.a, I.C.2.d, I.C.2.m).

    See the Table of Neoplasms entries · Guide: Active cancer vs history of cancer →

Choose the right path

  1. Does the record document the detail a more specific sibling code needs?
    Yes → Review the specific siblings in this subcategory.
    No → Continue — C45.9 is appropriate when the documentation goes no further.

    ReviewC45.0, C45.1, C45.2, C45.7

Consider C45.9. Then confirm the code is valid for the date of service in the Verify section.

Documentation check

The provider’s diagnostic statement
Codes are assigned from the provider’s documented diagnosis, not from clinical criteria, test values or a medication list (Guidelines I.A.19).
Anatomical site
At the most specific level the record states; a site the classification separates cannot be assumed from a procedure or a measurement.
Behavior and current-versus-history status
Malignant, in situ, benign or uncertain; primary or secondary; current disease or personal history (Guidelines I.C.2.m).
Any detail beyond this code’s title
What the record states that a more specific sibling code would capture — or its absence, which itself supports the unspecified code.

Coding decision scenarios

Pattern scenarios for this code’s structure — decision rules, not clinical cases

Documentation: The provider documents the condition in the terms of this code’s title and records no further detail.

Coding question: Is a more specific sibling code supportable?

Path: Review the specific siblings in this subcategory and what each requires the record to state.

Reason: A more specific code needs documentation of the distinguishing element; without it the unspecified code is appropriate, and a provider query is the route to specificity (Guidelines I.A.9.b, I.B.18).

ReviewC45.0, C45.1, C45.2, C45.7

Every row is derived from this code’s own record — its title, tabular notes, 7th-character family and same-category siblings — with fixed MedCoder wording; nothing is inferred about a patient. The official notes and guideline text are in the sections each row links to, and they control.

Code Overview

Mesothelioma, unspecified is a billable ICD-10-CM diagnosis code (C45.9).

MedCoder summary Summary composed by MedCoder from this code's official ICD-10-CM record. The tabular instructional notes themselves appear verbatim below.

Indexed Clinical Terms (5)

Official source data — entries quoted as published, in the Index’s own lookup phrasing

Clinical term phrases from the official ICD-10-CM Index to Diseases and Injuries that map to this code. These are alphabetic-index entries shown as the Index writes them — lookup phrasing, not necessarily the wording of a final diagnosis.

Verify Before Coding

  • No Medicare Code Editor or MS-DRG Definitions Manual restrictions apply to this code.

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim in Claim Check.

Relationships & Classification

MedCoder structured relationships — computed from published CMS and AHRQ datasets

Other codes that name C45.9 or its code family, from the CMS ICD-10-CM tabular instructional notes. Tabular-note edges are stored at the code family level that carries each note.

Referenced by 10 Excludes1 notes: C30 — Malignant neoplasm of nasal cavity and middle ear (via C45.-), C30-C39 — Malignant neoplasms of respiratory and intrathoracic organs (C30-C39) (via C45.-), C31 — Malignant neoplasm of accessory sinuses (via C45.-), C32 — Malignant neoplasm of larynx (via C45.-), C33 — Malignant neoplasm of trachea (via C45.-), C34 — Malignant neoplasm of bronchus and lung (via C45.-), C37 — Malignant neoplasm of thymus (via C45.-), C38 — Malignant neoplasm of heart, mediastinum and pleura (via C45.-), C39 — Malignant neoplasm of other and ill-defined sites in the respiratory system and intrathoracic organs (via C45.-), C48 — Malignant neoplasm of retroperitoneum and peritoneum (via C45.-).

These codes’ tabular lists mark this diagnosis as mutually exclusive — not reported together unless the conditions are documented as unrelated.

Referenced by 1 Excludes2 note: C49 — Malignant neoplasm of other connective and soft tissue (via C45.-).

These codes’ tabular lists name this diagnosis as distinct — both may be reported when both are documented.

MS-DRG Grouper Relationships (FY2027)

Potential MS-DRG participation — not a DRG assignment.

FY2027 MS-DRG: not on the CMS CC/MCC list — as a secondary diagnosis this code does not change MS-DRG severity for that release.

Named in the grouper logic of 8 MS-DRGs: DRG 826 (MDC 17), DRG 827 (MDC 17), DRG 828 (MDC 17), DRG 829 (MDC 17), DRG 830 (MDC 17), DRG 843 (MDC 17), DRG 844 (MDC 17), DRG 845 (MDC 17).

From the CMS MS-DRG Definitions Manual (Appendices B and C). Actual DRG assignment depends on the complete claim.

Clinical classification (AHRQ CCSR):NEO067 — Mesothelioma (default).

Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality.

Related Codes

Same CMS-HCC risk category (V28)

CMS maps these diagnoses to the same Hierarchical Condition Category (Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers) for risk-adjusted payment.

C45.0 — Mesothelioma of pleura, C45.1 — Mesothelioma of peritoneum, C45.2 — Mesothelioma of pericardium, C45.7 — Mesothelioma of other sites, C84.40 — Peripheral T-cell lymphoma, not elsewhere classified, unspecified site, C84.41 — Peripheral T-cell lymphoma, not elsewhere classified, lymph nodes of head, face, and neck, C84.42 — Peripheral T-cell lymphoma, not elsewhere classified, intrathoracic lymph nodes, C84.43 — Peripheral T-cell lymphoma, not elsewhere classified, intra-abdominal lymph nodes, C84.44 — Peripheral T-cell lymphoma, not elsewhere classified, lymph nodes of axilla and upper limb, C84.45 — Peripheral T-cell lymphoma, not elsewhere classified, lymph nodes of inguinal region and lower limb, C84.46 — Peripheral T-cell lymphoma, not elsewhere classified, intrapelvic lymph nodes, C84.47 — Peripheral T-cell lymphoma, not elsewhere classified, spleen, C84.48 — Peripheral T-cell lymphoma, not elsewhere classified, lymph nodes of multiple sites, C84.49 — Peripheral T-cell lymphoma, not elsewhere classified, extranodal and solid organ sites, C84.4A — Peripheral T-cell lymphoma, not elsewhere classified, in remission, C84.70 — Anaplastic large cell lymphoma, ALK-negative, unspecified site, C84.71 — Anaplastic large cell lymphoma, ALK-negative, lymph nodes of head, face, and neck, C84.72 — Anaplastic large cell lymphoma, ALK-negative, intrathoracic lymph nodes, C84.73 — Anaplastic large cell lymphoma, ALK-negative, intra-abdominal lymph nodes, C84.74 — Anaplastic large cell lymphoma, ALK-negative, lymph nodes of axilla and upper limb, +47 more

Related risk categories

These categories interact through CMS's HCC hierarchy — one can suppress the other's risk-adjustment weight when both are present on a claim.

Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic, Cancer Metastatic to Bone, Other and Unspecified Metastatic Cancer; Acute Leukemia Except Myeloid, Lung and Other Severe Cancers, Lymphoma and Other Cancers, Bladder, Colorectal, and Other Cancers, Prostate, Breast, and Other Cancers and Tumors

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical category (Mesothelioma).

C45.0 — Mesothelioma of pleura, C45.1 — Mesothelioma of peritoneum, C45.2 — Mesothelioma of pericardium, C45.7 — Mesothelioma of other sites

Same Index main term, other category

The ICD-10-CM Index to Diseases and Injuries files this code under the main term “Mesothelioma”; these codes share that main term but sit in a different category of the Tabular List.

D19.0 — Benign neoplasm of mesothelial tissue of pleura (benign, pleura), D19.1 — Benign neoplasm of mesothelial tissue of peritoneum (benign, omentum), D19.7 — Benign neoplasm of mesothelial tissue of other sites (benign, specified site NEC), D19.9 — Benign neoplasm of mesothelial tissue, unspecified (benign, unspecified site), D48.4 — Neoplasm of uncertain behavior of peritoneum (cystic)

Lab tests where this diagnosis supports Medicare coverage (NCD)

Medicare's National Coverage Determination (NCD) program lists this diagnosis as medical justification for these lab tests.

Iron Panel

Contextual Map

Every relationship of C45.9 in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Run C45.9 with these 9 related codes in Claim Check

Hierarchy

Referenced by Excludes1 notes (10)

Referenced by Excludes2 notes

Clinical classification (CCSR)

Risk adjustment (CMS-HCC)

  • HCC 19 — Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers [CMS-HCC]: “Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers — supersedes HCC 20 (Lung and Other Severe Cancers), HCC 21 (Lymphoma and Other Cancers), HCC 22 (Bladder, Colorectal, and Other Cancers), HCC 23 (Prostate, Breast, and Other Cancers and Tumors)”— CMS-HCC V28 · 2026

MS-DRG Grouper

MDC crossing

  • MDC 17 — Myeloproliferative Diseases and Disorders, Poorly Differentiated Neoplasms[MDC crossing]: “Myeloproliferative Diseases and Disorders, Poorly Differentiated Neoplasms — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs. 4,735 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2027

Index entries

  • Mesothelioma (malignant)[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Mesothelioma (malignant), biphasic[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Mesothelioma (malignant), epithelioid[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Mesothelioma (malignant), fibrous[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Mesothelioma (malignant), site classification, unspecified[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026

Nearest codes

Change history

  • FY2016 — In the code set at ICD-10-CM adoption [Change history]— CMS release files (code change ledger) · icd10cm-fy2016

Sources for this page

Codes, titles, notes, index terms and mappings on this page are transcribed from the datasets below. Relationships MedCoder computed and text MedCoder wrote are labelled where they appear.

Code, title, tabular notes and index terms Official source data
CMS/CDC ICD-10-CM FY2027 tabular list, index and tables, effective October 1, 2026 Release, file and checksum · Publisher’s page
Claim edits Official source data
CMS Definitions of Medicare Code Edits — v44.0 (October 2026) Release, file and checksum · Publisher’s page
Inpatient payment groups Official source data
CMS MS-DRG Definitions Manual (incl. Appendix B diagnosis index, Appendix C CC/MCC list, Appendix E procedure index) and IPPS Final Rule tables — v44 Release, file and checksum · Publisher’s page
Risk adjustment Official source data
2026 Mid-Year Final ICD-10 Mappings + Model Software (cms.gov/files/zip/2026-midyear-final-icd-10-mappings.zip, 2026-midyear-final-model-software.zip) — CMS-HCC V28, PY2026 mid-year final release Release, file and checksum · Publisher’s page
Change history and date-of-service validity Official source data
CMS ICD-10-CM release addenda, ingested release by release into the change ledger Release, file and checksum · Publisher’s page
Comparisons, relationships and the contextual map MedCoder structured relationship
Computed by MedCoder from the tabular notes and tables above; every derived relationship is marked as derived where it appears
Summary and FAQ answers MedCoder explanation
Written by MedCoder to explain the sources above: drafted with AI assistance, checked by a person against the release files, and labelled as MedCoder text where it appears. Not official text.

Labels on this page: Official source data · MedCoder structured relationship · MedCoder explanation. How to read the labels · All data sources and release dates

Cite this page

Reference this page in a research guide, syllabus or article. The release is included because code content changes each year.

MedCoder.ai. "C45.9 — Mesothelioma, unspecified." ICD-10-CM FY2027. https://medcoder.ai/icd10/code/c45.9-mesothelioma-unspecified

Change history

  • FY2016 — October 1, 2015
    In the code set at ICD-10-CM adoption
    Mesothelioma, unspecified

No changes since FY2016 — additions, deletions, description changes and billable-status changes are tracked through FY2027, and none are recorded for this code. Note changes are tracked from FY2027 only.

Nearest Codes in This Family

Official ICD-10-CM classifications closest to C45.9 in its code family, with their registry titles.

View all codes in the C45 family