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C38.3 ICD-10-CM Code: Malignant neoplasm of mediastinum, part unspecified

C38.3 maps to CMS-HCC V28 21. A source-labeled RAF reference is available. Documentation must support MEAT. MEAT criteria · RAF Calculator · HCC coding software

ICD-10-CM Code View

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FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of respiratory and intrathoracic organs (C30-C39)

C38.3

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

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.

Buddy the Bee presenting code insight

Buddy Insight

Unspecified mediastinal cancer is used when the specific mediastinal compartment (anterior, posterior, middle) cannot be determined from documentation.

CMS-HCC V28

HCC 21

Code-level coefficient reference

CMS-HCC V24

Historical

Historical

Not used for CY2026 payment

ACA/HHS

HCC 011

Code-level coefficient reference

ESRD/PACE

HCC 11

Code-level coefficient reference

RXHCC

HCC 22

Code-level coefficient reference

Code Book Path

Official
C38Malignant neoplasm of heart, mediastinum and pleura
C38.3Malignant neoplasm of mediastinum, part unspecified

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for C38.3 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C38.3 in this effective period.

Related Child Codes

Official
C38.0Malignant neoplasm of heart
C38.1Malignant neoplasm of anterior mediastinum
C38.2Malignant neoplasm of posterior mediastinum
C38.4Malignant neoplasm of pleura
C38.8Malignant neoplasm of overlapping sites of heart, mediastinum and pleura

Includes

Official

ICD-10-CM does not list Includes notes for C38.3 in this effective period.

Excludes 1

Official
  • mesothelioma (C45.-)

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C38.3 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C38.3 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C38.3 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance
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

MEAT Support

HCC Buddy guidance
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

Audit Caution

HCC Buddy guidance
Using unspecified when CT or MRI clearly shows the mediastinal compartment
Not querying the provider when imaging almost always identifies the compartment
Coding lymphoma as unspecified mediastinal cancer instead of lymphoma-specific codes
Failing to review cross-sectional imaging that readily identifies anterior vs. posterior vs. middle

Common Mistakes

HCC Buddy guidance
C38.1 — Anterior mediastinum: Most common location for mediastinal tumors
C38.2 — Posterior mediastinum: Second most common; distinct tumor types
C37 — Thymic cancer: If thymic origin is confirmed, use the more specific code
C38.8 — Overlapping sites: Use when multiple intrathoracic sites are involved

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is C38.3 an HCC code?

Yes. C38.3 (Malignant neoplasm of mediastinum, part unspecified) maps to HCC 21, Lymphoma and Other Cancers under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.671. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.

Coder answer: C38.3 is billable and maps to V28 HCC 21, Lymphoma and Other Cancers. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code
C38.3
Description
Malignant neoplasm of mediastinum, part unspecified
HCC (V28)
HCC 21 — Lymphoma and Other Cancers
RAF reference coefficient
0.671
Billable
Yes
Payment year
2026

HCC Category Mapping

V28HCC 21, Lymphoma and Other Cancers
0.671
ESRDHCC 11, Colorectal/Bladder/and Other Cancers
Not separately weighted
RxHCCHCC 22, Prostate, Breast, Bladder, and Other Cancers and Tumors
Not separately weighted

These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. Weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.

Work C38.3 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

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.

Coder workflow notes

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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 Lymphoma and Other Cancers (HCC 21) with a source-labeled community, non-dual, aged reference coefficient of 0.671. No V24 mapping is shown for C38.3; use the applicable model and payment year when reviewing the V28 mapping. 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. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.

This is a less specific code; use only when anterior, posterior, or other mediastinal locations cannot be identified. Because C38.3 maps to an HCC category, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) before the diagnosis is used for risk adjustment. 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, source-labeled coefficient references, 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

Commonly Confused Codes

  • •C38.1: Anterior mediastinum: Most common location for mediastinal tumors
  • •C38.2: Posterior mediastinum: Second most common; distinct tumor types
  • •C37: Thymic cancer: If thymic origin is confirmed, use the more specific code
  • •C38.8: Overlapping sites: Use when multiple intrathoracic sites are involved

Child Codes

C38.0Malignant neoplasm of heart
HCC 20
C38.1Malignant neoplasm of anterior mediastinum
HCC 21
C38.2Malignant neoplasm of posterior mediastinum
HCC 21
C38.3Malignant neoplasm of mediastinum, part unspecified
HCC 21
C38.4Malignant neoplasm of pleura
HCC 20
C38.8Malignant neoplasm of overlapping sites of heart, mediastinum and pleura
HCC 21

Code Hierarchy

└C38Malignant neoplasm of heart, mediastinum and pleura└C38.3Malignant neoplasm of mediastinum, part unspecified
└C38.3Malignant neoplasm of mediastinum, part unspecified

Because C38.3 maps to an HCC category, the documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) before the diagnosis is used for risk adjustment.

C38.3 maps to CMS-HCC V28 category 21, Lymphoma and Other Cancers. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works. The mapping identifies a payment HCC category for C38.3. Review its source-labeled HCC coefficient above, check the RAF Calculator with complete member context for CMS-HCC V28 PY2026, and confirm the documentation the chart needs before the code is submitted. HCC Buddy shows no RAF score unless every required source and calculation check passes.

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Open C38.3 in the Code Book for the full Index-to-Tabular path, MEAT checklist, and V28 HCC mapping, or in the Encoder to code from a keyword search. Pro includes 7 days to try everything, no card required.

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