C38.3
BillableMalignant neoplasm of mediastinum, part unspecified
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C38.3 an HCC code?
Yes. C38.3 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 C38.3
For C38.3 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 C38.3 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C38.3 is the ICD-10-CM diagnosis code for malignant neoplasm of mediastinum, part unspecified. Cancer in the mediastinum (the central area of the chest between the lungs) when the specific part cannot be determined. C38.3 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, C38.3 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, C38.3 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.
This is a less specific code; use only when anterior, posterior, or other mediastinal locations cannot be identified. Because C38.3 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 C38.3 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This is a less specific code; use only when anterior, posterior, or other mediastinal locations cannot be identified
- •Review imaging reports to determine if a more specific mediastinal site code applies
Clinical Significance
Unspecified mediastinal cancer is used when the specific mediastinal compartment (anterior, posterior, middle) cannot be determined from documentation. Since different compartments harbor completely different tumor types with different treatment approaches, this code represents a significant documentation gap that should prompt imaging review and provider query.
Documentation Requirements
- ✓Pathology or clinical confirmation of mediastinal malignancy
- ✓Evidence that imaging was reviewed for compartment specification
- ✓Provider query for specific mediastinal location
- ✓Treatment status and disease stage
- ✓Reason the specific compartment cannot be determined