C38.1
BillableMalignant neoplasm of anterior mediastinum
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C38.1 an HCC code?
Yes. C38.1 maps to Breast, Prostate, Colorectal and Other Cancers and Tumors under the CMS-HCC V28 risk adjustment model (and Colorectal, Bladder, and Other Cancers under V24).
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.
MEAT Criteria for C38.1
For C38.1 to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically — it has to be re-documented and supported each calendar year.
- MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
- EEvaluate: test results, medication response, or physical findings reviewed by the provider
- AAssess: explicit mention in the assessment or plan with acknowledgment of status
- TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis
Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed C38.1 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C38.1 is the ICD-10-CM diagnosis code for malignant neoplasm of anterior mediastinum. This code describes cancer that starts in the anterior (front) mediastinum, which is the space in the chest between the lungs that contains the heart, major blood vessels, and other structures. It is a malignant (cancerous) tumor in this specific location. C38.1 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of respiratory and intrathoracic organs (c30-c39).
Under the CMS-HCC V28 risk adjustment model, C38.1 maps to Breast, Prostate, Colorectal and Other Cancers and Tumors (HCC 21) with a community, non-dual, aged base RAF weight of 0.545. Under the older CMS-HCC V24 model, C38.1 maps to Colorectal, Bladder, and Other Cancers (HCC 11) with a community, non-dual, aged base RAF weight of 0.306. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.
Verify the histological type of the malignancy (e.g., lymphoma, thymoma, germ cell tumor) as this may require additional coding with laterality or histology codes. Because C38.1 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for C38.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Verify the histological type of the malignancy (e.g., lymphoma, thymoma, germ cell tumor) as this may require additional coding with laterality or histology codes
- •Ensure documentation specifies 'anterior mediastinum' to distinguish from other mediastinal locations (middle C38.2 or posterior C38.3), as treatment and prognosis differ significantly
Clinical Significance
Anterior mediastinal cancers include a diverse group of tumors — thymomas, germ cell tumors, lymphomas, and thyroid tumors extending into the mediastinum. The anterior mediastinum is the most common location for mediastinal masses. Accurate site coding is essential because treatment varies dramatically by histological type.
Documentation Requirements
- ✓Pathology confirming malignancy and histological type
- ✓Imaging specifying anterior mediastinal location
- ✓Assessment for compression of adjacent structures (superior vena cava, airway)
- ✓Tumor markers (AFP, beta-HCG for germ cell tumors; LDH for lymphoma)
- ✓Differentiation from thymic, thyroid, or lymphomatous origin