What is ICD-10 code C77.1?

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. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C77.1 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C77.1 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. C77.1 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. C77.1 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

Which HCC does C77.1 map to under V28?

C77.1 maps to CMS-HCC V28 17 (Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic). The category number and label come from the CMS-HCC V28 model file for payment year 2026.

What does C77.1 pay in RAF?

C77.1 carries a community, non-dual, aged (CNA) RAF weight of 4.209 under CMS-HCC V28 for payment year 2026. The weight comes from the CMS V28 relative-factor file, not a hand-typed table.

What is the V28 vs V24 difference for C77.1?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. For C77.1, V28 maps to Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic at RAF 4.209 while V24 mapped to Metastatic Cancer and Acute Leukemia at RAF 2.659. Both models can still appear in legacy data and in payer-specific lookback periods.

What documentation supports C77.1?

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 Because C77.1 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score. See the MEAT criteria checklist at /meat-criteria for what Monitor, Evaluate, Assess, or Treat looks like in a note. MEAT is generic documentation evidence, not a payer-specific rule.

2026 ICD-10-CM C77.1: Secondary

C77.1 maps to CMS-HCC V28 17 (RAF 4.209). Documentation must support MEAT. MEAT criteria · RAF calculator · free HCC coding tools

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Code lookupC77.1Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of ill-defined, other secondary and unspecified sites (C76-C80)

C77.1

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

Secondary and unspecified malignant neoplasm of intrathoracic lymph nodes

Cancer that has spread to or originated in the lymph nodes inside the chest cavity.

Buddy Insight

Secondary and unspecified malignant neoplasm of intrathoracic lymph nodes represents metastatic disease to mediastinal, hilar, or other thoracic lymph nodes.

CMS-HCC V28

Mapped

HCC 17

Cancer Metastatic to Lung, Li...

RAF 4.209

CMS-HCC V24

Mapped

HCC 8

Metastatic Cancer and Acute L...

RAF 2.659

ACA/HHS

Mapped

HCC 8

HHS-HCC 8

Varies by metal level

ESRD/PACE

Mapped

HCC 8

Metastatic Cancer and Acute L...

RAF 0.353

RXHCC

Mapped

HCC 20

Cancer, Liver and Intrahepati...

RAF 0.491

Code Book Path

Official

C77Secondary and unspecified malignant neoplasm of lymph nodes

C77.1Secondary and unspecified malignant neoplasm of intrathoracic lymph nodes

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for C77.1 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C77.1 in this effective period.

Related Child Codes

Official

C77.0Secondary and unspecified malignant neoplasm of lymph nodes of head, face and neck

C77.2Secondary and unspecified malignant neoplasm of intra-abdominal lymph nodes

C77.3Secondary and unspecified malignant neoplasm of axilla and upper limb lymph nodes

C77.4Secondary and unspecified malignant neoplasm of inguinal and lower limb lymph nodes

C77.5Secondary and unspecified malignant neoplasm of intrapelvic lymph nodes

Includes

Official

ICD-10-CM does not list Includes notes for C77.1 in this effective period.

Excludes 1

Official

malignant neoplasm of lymph nodes, specified as primary (C81-C86, C88, C96.-)
mesentery metastasis of carcinoid tumor (C7B.04)
secondary carcinoid tumors of distant lymph nodes (C7B.01)

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C77.1 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C77.1 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C77.1 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

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)

MEAT Support

HCC Buddy guidance

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)

Audit Caution

HCC Buddy guidance

Coding mediastinal lymphoma as secondary lymph node malignancy — lymphoma is a primary process

Not separately coding the primary malignancy site

Confusing reactive hilar lymphadenopathy (e.g., from sarcoidosis) with metastatic disease

Using this code when pulmonary lymph nodes are involved as direct extension of lung cancer rather than true metastasis

Common Mistakes

HCC Buddy guidance

C77.0 — Head, face, neck lymph nodes: Different regional lymph node group

C77.8 — Multiple regional lymph nodes: Use when multiple regions are involved

C38.1-C38.3 — Malignant neoplasm of mediastinum: Primary mediastinal tumor, not metastatic lymph nodes

C81-C86 — Lymphomas: Primary lymph node malignancy, not secondary metastatic disease

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 C77.1 an HCC code?

Yes. C77.1 (Secondary and unspecified malignant neoplasm of intrathoracic lymph nodes) maps to Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic under the CMS-HCC V28 risk adjustment model (and Metastatic Cancer and Acute Leukemia under V24), with a community non-dual aged RAF of 4.209. It is billable for payment year 2026.

Coder answer: C77.1 is billable and maps to V28 HCC 17, Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: C77.1
Description: Secondary and unspecified malignant neoplasm of intrathoracic lymph nodes
HCC (V28): HCC 17 — Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic
RAF: 4.209
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 17, Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic

4.209

V24HCC 8, Metastatic Cancer and Acute Leukemia

2.659

ESRDHCC 8, Metastatic Cancer and Acute Leukemia

0.353

RxHCCHCC 20, Cancer, Liver and Intrahepatic Bile Duct

0.491

Each model's RAF is its CMS base weight for that model's standard population, so 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 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.

Work C77.1 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

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.

Coder workflow notes

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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 Cancer Metastatic to Lung, Liver, Brain, and Other Organs; Acute Myeloid Leukemia Except Promyelocytic (HCC 17) with a community, non-dual, aged base RAF weight of 4.209. Under the older CMS-HCC V24 model, C77.1 maps to Metastatic Cancer and Acute Leukemia (HCC 8) with a community, non-dual, aged base RAF weight of 2.659. 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

Commonly Confused Codes

•C77.0: Head, face, neck lymph nodes: Different regional lymph node group
•C77.8: Multiple regional lymph nodes: Use when multiple regions are involved
•C38.1-C38.3: Malignant neoplasm of mediastinum: Primary mediastinal tumor, not metastatic lymph nodes
•C81-C86: Lymphomas: Primary lymph node malignancy, not secondary metastatic disease
•R59.0: Localized enlarged lymph nodes: Non-malignant lymphadenopathy