2027 ICD-10-CM Diagnosis Code C37Malignant neoplasm of thymus
ICD-10-CM Codes›C00–D49›C30-C39›C37
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Risk Adjusts — HCC 21
- Chronic Condition
C37 is a billable ICD-10-CM diagnosis code for malignant neoplasm of thymus. 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. 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 2 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Endocrine system cancers - thymus.
For Medicare Advantage risk adjustment, C37 maps to CMS-HCC Category 21 (Lymphoma and Other Cancers) under the V28 model, adding a risk factor of about 0.671 for a community, non-dual, aged beneficiary in payment year 2027.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
C37 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 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
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to C37: its own notes plus those printed at block C30-C39 and Chapter 2. A note printed at a category, block or chapter applies to every code under it.
Includes
Further defines, or gives examples of, the content of the category.
- malignant neoplasm of middle ear
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
- malignant carcinoid tumor of the thymus (C7A.091)
- mesothelioma (C45.-)
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 C37, its category, or a range that includes it.
Applicable To 2
These notes mention C37.
Excludes1 2
These codes carry an Excludes1 note naming C37: they are not reported together with it, unless the two conditions are unrelated.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
Carcinoma (malignant) See Also: Neoplasm, by site, malignant;
thymic C37
Thymoma See Also: Neoplasm, thymus, by type;
malignant C37
metaplastic C37
sclerosing C37
type A C37
type AB C37
type B1 C37
type B2 C37
type B3 C37
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Malignant Thymus Neoplasm
a primary or metastatic malignant neoplasm involving the thymus. this category includes malignant thymomas, thymic lymphomas, primary thymic carcinomas, and metastatic carcinomas from other anatomic sites.
Table of NeoplasmsClinical
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.
Code HistoryHistory
Questions About C37Overview
What is the ICD-10 code for malignant neoplasm of thymus?
The ICD-10-CM code for malignant neoplasm of thymus is C37. It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
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, 2026 through September 30, 2027.
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 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.
Is C37 a CC or MCC?
CMS lists C37 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 2 closely related codes in its exclusion list.
Can C37 be reported with C7A.091?
Not as a rule. The Excludes1 note on C37 lists "malignant carcinoid tumor of the thymus (C7A.091)". 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 C37?
C37 (malignant neoplasm of thymus) maps to CMS-HCC Category 21 (Lymphoma and Other Cancers), commonly written as HCC 21, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It mapped to HCC 11 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 C37 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, C37 adds a risk adjustment factor of about 0.671 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.493 to 0.739 depending on the payment segment). A more severe related category (HCC 17, HCC 18, HCC 19, and HCC 20) supersedes it when both are reported. See the full factor table on the HCC 21 category page.
