2026 ICD-10-CM Diagnosis Code D38.4Neoplasm of uncertain behavior of thymus

ICD-10-CM Codes›C00–D49›D37-D48›D38

ICD-10-CM D38.4
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

D38.4 is a billable ICD-10-CM diagnosis code for neoplasm of uncertain behavior of thymus. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 180 through 182. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Neoplasms of unspecified nature or uncertain behavior.

Code Identity

ICD-10-CM Code
D38.4
Billable Status
Yes — Valid for Submission
Code Describes
Neoplasm of uncertain behavior of thymus
Short Description
Neoplasm of uncertain behavior of thymus
Same as the full description in the CMS dataset.
Parent Code
D38
Neoplasm of uncertain behavior of middle ear and respiratory and intrathoracic organs

Code Classification

ChapterC00–D49Neoplasms
SectionD37-D48Neoplasms of uncertain behavior, polycythemia vera and myelodysplastic syndromes
CategoryD38Neoplasm of uncertain behavior of middle ear and respiratory and intrathoracic organs
This CodeD38.4Neoplasm of uncertain behavior of thymus

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Neoplasm of uncertain behavior of thymus

Clinical ClassificationClinical

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

CCSR NEO072
Neoplasms of unspecified nature or uncertain behavior
Default principal diagnosis: inpatient Yes · outpatient Yes

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

Convert D38.4 to ICD-9-CMHistory

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

ICD-9-CM
235.8 Unc behav neo pleura
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 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About D38.4Overview

Is D38.4 a billable code?

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

What MS-DRG does D38.4 group to?

When neoplasm of uncertain behavior of thymus is the principal diagnosis on an inpatient stay, it groups to MS-DRG 180, 181, 182, with relative weights from 0.7440 to 1.7660 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of D38.4?

Under the General Equivalence Mappings, neoplasm of uncertain behavior of thymus converts to ICD-9-CM 235.8 (unc behav neo pleura). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.