What is ICD-10 code C77.4?

C77.4 is the ICD-10-CM diagnosis code for Secondary and unspecified malignant neoplasm of inguinal and lower limb lymph nodes. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C77.4 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C77.4 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. C77.4 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. C77.4 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.

What is the V28 vs V24 difference for C77.4?

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 C77.4, V28 maps to Metastatic Cancer to Peritoneum and Other Specified Sites at RAF 0.368 while V24 mapped to Metastatic Cancer and Acute Leukemia at RAF 2.484. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting C77.4?

Code the primary malignancy separately when identified; this code specifically indicates lymph node involvement in the inguinal and lower limb regions Do not use this code for primary lymphomas originating in these nodes; use appropriate lymphoma codes instead Because C77.4 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.

C77.4 ICD-10 Code: Secondary and unspecified

ICD-10-CM Code View

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Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.

Code lookupC77.4Effective 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)

C77.4

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

Secondary and unspecified malignant neoplasm of inguinal and lower limb lymph nodes

Cancer that has spread to the lymph nodes in the groin and lower leg area, either as a secondary spread from another cancer or when the primary source is unknown.

Buddy Insight

Secondary and unspecified malignant neoplasm of inguinal and lower limb lymph nodes represents metastatic cancer involving the groin or lower extremity lymph nodes.

CMS-HCC V28

Mapped

HCC 18

Metastatic Cancer to Peritone...

RAF 0.368

CMS-HCC V24

Mapped

HCC 8

Metastatic Cancer and Acute L...

RAF 2.484

ACA/HHS

Not risk-adjusted for this model/period.

RAF 0

ESRD/PACE

Mapped

HCC 8

Metastatic Cancer and Acute L...

RAF 0.0

RXHCC

Mapped

HCC 20

Cancer, Liver and Intrahepati...

RAF 0.0

Code Trumping

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Code Book Path

Official

C77Secondary and unspecified malignant neoplasm of lymph nodes

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

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for C77.4 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C77.4 in this effective period.

Related Child Codes

Official

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

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

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

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

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

Includes

Official

ICD-10-CM does not list Includes notes for C77.4 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 C77.4 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C77.4 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C77.4 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Pathology confirming malignant involvement of inguinal or lower limb lymph nodes

Identification and separate coding of the primary malignancy

Number of involved nodes and extent of disease

Laterality of inguinal nodal involvement

MEAT Support

HCC Buddy guidance

Pathology confirming malignant involvement of inguinal or lower limb lymph nodes

Identification and separate coding of the primary malignancy

Number of involved nodes and extent of disease

Laterality of inguinal nodal involvement

Audit Caution

HCC Buddy guidance

Coding inguinal lymphoma as metastatic disease instead of primary lymphoma

Not separately coding the primary malignancy driving the nodal metastasis

Confusing infected inguinal lymph nodes with metastatic disease

Not distinguishing inguinal (C77.4) from intrapelvic (C77.5) lymph node involvement

Common Mistakes

HCC Buddy guidance

C77.3 — Axillary and upper limb lymph nodes: Upper extremity, not lower

C77.5 — Intrapelvic lymph nodes: Internal pelvic nodes vs. inguinal/lower limb nodes

C63.2 — Malignant neoplasm of scrotum: Primary scrotal malignancy, not inguinal nodes

C81-C86 — Lymphomas: Primary lymph node malignancy

Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.

Is C77.4 an HCC code?

Yes. C77.4 maps to Metastatic Cancer to Peritoneum and Other Specified Sites under the CMS-HCC V28 risk adjustment model (and Metastatic Cancer and Acute Leukemia under V24).

HCC Category Mapping

V28HCC 18, Metastatic Cancer to Peritoneum and Other Specified Sites

0.368

V24HCC 8, Metastatic Cancer and Acute Leukemia

2.484

ESRDHCC 8, Metastatic Cancer and Acute Leukemia

0.000

RxHCCHCC 20, Cancer, Liver and Intrahepatic Bile Duct

0.000

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 C77.4

For C77.4to 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 C77.4 during that encounter, not just copy-forwarded from a problem list.

What This Code Means

C77.4 is the ICD-10-CM diagnosis code for secondary and unspecified malignant neoplasm of inguinal and lower limb lymph nodes. Cancer that has spread to the lymph nodes in the groin and lower leg area, either as a secondary spread from another cancer or when the primary source is unknown. C77.4 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, C77.4 maps to Metastatic Cancer to Peritoneum and Other Specified Sites (HCC 18) with a community, non-dual, aged base RAF weight of 0.368. Under the older CMS-HCC V24 model, C77.4 maps to Metastatic Cancer and Acute Leukemia (HCC 8) with a community, non-dual, aged base RAF weight of 2.484. 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.

Code the primary malignancy separately when identified; this code specifically indicates lymph node involvement in the inguinal and lower limb regions. Because C77.4 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 C77.4 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Code the primary malignancy separately when identified; this code specifically indicates lymph node involvement in the inguinal and lower limb regions
•Do not use this code for primary lymphomas originating in these nodes; use appropriate lymphoma codes instead

Clinical Significance

Secondary and unspecified malignant neoplasm of inguinal and lower limb lymph nodes represents metastatic cancer involving the groin or lower extremity lymph nodes. This commonly occurs with melanoma of the lower extremity, vulvar cancer, penile cancer, and anal cancer. Inguinal lymph node dissection is a common staging procedure for several of these malignancies.

Documentation Requirements

✓Pathology confirming malignant involvement of inguinal or lower limb lymph nodes
✓Identification and separate coding of the primary malignancy
✓Number of involved nodes and extent of disease
✓Laterality of inguinal nodal involvement
✓Treatment plan including any planned lymph node dissection

Commonly Confused Codes

•C77.3 — Axillary and upper limb lymph nodes: Upper extremity, not lower
•C77.5 — Intrapelvic lymph nodes: Internal pelvic nodes vs. inguinal/lower limb nodes
•C63.2 — Malignant neoplasm of scrotum: Primary scrotal malignancy, not inguinal nodes
•C81-C86 — Lymphomas: Primary lymph node malignancy
•L04.3 — Acute lymphadenitis of lower limb: Infectious/inflammatory, not malignant