C77.1
BillableSecondary and unspecified malignant neoplasm of intrathoracic lymph nodes
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C77.1 an HCC code?
Yes. C77.1 maps to Metastatic Cancer and Acute Leukemia under the CMS-HCC V28 risk adjustment model (and Metastatic Cancer and Acute Leukemia 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 C77.1
For C77.1 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 C77.1 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C77.1 is the ICD-10-CM diagnosis code for secondary and unspecified malignant neoplasm of intrathoracic lymph nodes. Cancer that has spread to or originated in the lymph nodes inside the chest cavity. C77.1 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of ill-defined, other secondary and unspecified sites (c76-c80).
Under the CMS-HCC V28 risk adjustment model, C77.1 maps to Metastatic Cancer and Acute Leukemia (HCC 17) with a community, non-dual, aged base RAF weight of 0.368. Under the older V24 model, C77.1 mapped to the same category but with a base RAF weight of 2.484 — 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 applies to malignancies affecting intrathoracic (mediastinal and hilar) lymph nodes. Because C77.1 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 C77.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This code applies to malignancies affecting intrathoracic (mediastinal and hilar) lymph nodes
- •Document whether this represents secondary spread from another primary cancer or a primary lymph node malignancy
Clinical Significance
Secondary and unspecified malignant neoplasm of intrathoracic lymph nodes represents metastatic disease to mediastinal, hilar, or other thoracic lymph nodes. This is commonly seen with lung cancer, breast cancer, esophageal cancer, and lymphomas presenting with thoracic involvement. Accurate coding of intrathoracic nodal metastases significantly impacts risk adjustment and treatment planning.
Documentation Requirements
- ✓Imaging (CT chest, PET scan) confirming malignant lymphadenopathy in intrathoracic nodes
- ✓Pathology confirmation when available (mediastinoscopy, EBUS biopsy)
- ✓Identification and separate coding of the primary malignancy
- ✓Specific lymph node stations involved (mediastinal, hilar, paratracheal, subcarinal)
- ✓Treatment plan addressing metastatic nodal disease