ICD-10 Code C37 – Malignant neoplasm of thymus (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C37 – Malignant neoplasm of thymus
What it is
C37 identifies a malignant tumor arising in the thymus gland, which sits in the anterior mediastinum. Use it when documentation states thymic cancer or malignant neoplasm of thymus.
Clinical signs
Clinical features vary; refer to documentation. Thymic malignancies may be found on imaging or present with chest symptoms, such as cough, chest pain, or shortness of breath.
When to use this code
Use C37 when the provider documents a primary malignant neoplasm of the thymus. It is appropriate for confirmed thymic cancer, including pathology or imaging-supported diagnoses recorded by the clinician. If the site is uncertain or another mediastinal structure is named, check documentation before coding.
Do not use for
Do not use C37 for benign thymic tumors, thymic hyperplasia, or non-thymic mediastinal masses. If the record describes metastatic disease to the thymus, code the primary cancer elsewhere.
Coding tip
Confirm the tumor is primary to the thymus and not another mediastinal or metastatic lesion before assigning C37.