C34.00
BillableMalignant neoplasm of unspecified main bronchus
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C34.00 an HCC code?
Yes. C34.00 maps to Lung and Other Severe Cancers under the CMS-HCC V28 risk adjustment model (and Lung and Other Severe 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 C34.00
For C34.00 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 C34.00 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C34.00 is the ICD-10-CM diagnosis code for malignant neoplasm of unspecified main bronchus. Cancer of the main bronchus (the large airway that branches from the trachea into the lungs) when it is unclear which side or specific location is affected. C34.00 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, C34.00 maps to Lung and Other Severe Cancers (HCC 20) with a community, non-dual, aged base RAF weight of 0.000. Under the older V24 model, C34.00 mapped to the same category but with a base RAF weight of 0.973 — V28 recalibrated weights across the entire model. 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 code is used when the main bronchus is involved but laterality (left vs. right) is not specified. Because C34.00 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 C34.00 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
Clinical Significance
This code represents cancer of the main bronchus (carina region) without laterality specified. Main bronchial cancers are centrally located and often present with airway obstruction, hemoptysis, and post-obstructive pneumonia. These carry high RAF weight as severe cancers requiring aggressive multimodal treatment.
Documentation Requirements
- ✓Pathology confirmation with cell type (small cell, non-small cell, squamous, adenocarcinoma)
- ✓Bronchoscopy or imaging confirming main bronchus location
- ✓Evidence that laterality cannot be determined from available records
- ✓TNM staging including nodal and metastatic status
- ✓Treatment plan (surgical candidacy, chemotherapy, radiation)
Commonly Confused Codes
- •C34.01/C34.02 — Right/left main bronchus: Always assign laterality when documented; C34.00 is a fallback
- •C33 — Tracheal cancer: The boundary is at the carina; tumors above are tracheal
- •C34.10-C34.92 — Lobar lung cancers: Main bronchus is distinct from lobar or peripheral lung tumors
- •C78.00 — Secondary malignant neoplasm of lung: Ensure this is primary, not metastatic