2026 ICD-10-CM Diagnosis Code C37Malignant neoplasm of thymus

ICD-10-CM Codes›C00–D49›C30-C39›C37

ICD-10-CM C37
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

C37 is a billable ICD-10-CM diagnosis code for malignant neoplasm of thymus. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 826 through 830, 843 through 845. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Endocrine system cancers - thymus.

Code Identity

ICD-10-CM Code
C37
Billable Status
Yes — Valid for Submission
Code Describes
Malignant neoplasm of thymus
Chapter
C30-C39
Malignant neoplasms of respiratory and intrathoracic organs

Code Classification

ChapterC00–D49Neoplasms
SectionC30-C39Malignant neoplasms of respiratory and intrathoracic organs
CategoryC37Malignant neoplasm of thymus
This CodeC37Malignant neoplasm of thymus

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Malignant neoplasm of thymus gland
  • Malignant thymoma
  • Neuroendocrine carcinoma of thymus
  • Primary malignant neoplasm of thymus
  • Primary malignant thymoma
  • Primary small cell neuroendocrine carcinoma of thymus
  • Primary thymic carcinoma
  • Stage I: Grossly and microscopically encapsulated
  • Stage IIa: Microscopic transcapsular invasion
  • Stage IIb: Macroscopic capsular invasion into thymic or surrounding fat, or grossly adherent to, but not breaking through, mediastinal pleura or pericardium
  • Stage III: Macroscopic invasion of neighboring organs
  • Stage IVa: Pleural or pericardial dissemination
  • Stage IVb: Hematogenous or lymphatic dissemination
  • Thymic epithelial neoplasm stage finding
  • Thymoma
  • Thymoma type A
  • Thymoma type AB
  • Thymoma type B
  • Type C thymoma

Tabular List NotesGuidance

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

Type 1 Excludes

  • malignant carcinoid tumor of the thymus C7A.091

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.

    • Carcinoma(malignant)
      • thymic
    • Thymoma
      • malignant
    • Thymoma
      • metaplastic
    • Thymoma
      • sclerosing
    • Thymoma
      • type A
    • Thymoma
      • type AB
    • Thymoma
      • type B1
    • Thymoma
      • type B2
    • Thymoma
      • type B3

Clinical ClassificationClinical

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

CCSR NEO052
Endocrine system cancers - thymus
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Thymoma

    a neoplasm originating from thymic tissue, usually benign, and frequently encapsulated. although it is occasionally invasive, metastases are extremely rare. it consists of any type of thymic epithelial cell as well as lymphocytes that are usually abundant. malignant lymphomas that involve the thymus, e.g., lymphosarcoma, hodgkin's disease (previously termed granulomatous thymoma), should not be regarded as thymoma. (from stedman, 25th ed)

Table of NeoplasmsClinical

Anatomical sites in the Table of Neoplasms that reference this code family.

SiteMalig.
Primary		Malig.
Secondary		Ca
in situ		BenignUncertainUnspec.
thymus (gland)C37C79.89D09.3D15.0D38.4D49.89

Patient EducationClinical

Thymus Cancer

The thymus is a small organ in your upper chest, under your breastbone. Before birth and during childhood, the thymus helps the body make a type of white blood cell. These cells help protect you from infections.

Read the full article at MedlinePlus

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

Convert C37 to ICD-9-CMHistory

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

ICD-9-CM
164.0 Malignant neopl thymus
Exact Match The mapping is direct, with no qualifiers.

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 C37Overview

Is C37 (Malignant neoplasm of thymus) a billable code?

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

What MS-DRG does C37 group to?

When malignant neoplasm of thymus is the principal diagnosis on an inpatient stay, it groups to MS-DRG 826, 827, 828, 829, 830, 843, 844, 845, with relative weights from 0.8516 to 4.6778 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of C37?

Under the General Equivalence Mappings, malignant neoplasm of thymus converts to ICD-9-CM 164.0 (malignant neopl thymus). The mapping is a direct match.

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.