C77.4 ICD-10-CM Code: Secondary and unspecified malignant neoplasm of inguinal and lower limb lymph nodes
HCC Buddy Code Card
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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 guidanceSecondary 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
MappedHCC 18
RAF 2.341
CMS-HCC V24
MappedHCC 8
RAF 2.659
ACA/HHS
MappedHCC 8
Varies by metal level
ESRD/PACE
MappedHCC 8
RAF 0.353
RXHCC
MappedHCC 20
RAF 0.491
Code Book Path
Inclusion Terms
OfficialICD-10-CM does not list inclusion terms for C77.4 in this effective period.
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for C77.4 in this effective period.
Related Child Codes
Includes
OfficialICD-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
OfficialICD-10-CM does not list Code First sequencing instructions for C77.4 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for C77.4 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for C77.4 in this effective period.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
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 C77.4 an HCC code?
Yes. C77.4 (Secondary and unspecified malignant neoplasm of inguinal and lower limb lymph nodes) maps to Cancer Metastatic to Bone, Other and Unspecified Metastatic Cancer; Acute Leukemia Except Myeloid under the CMS-HCC V28 risk adjustment model (and Metastatic Cancer and Acute Leukemia under V24), with a community non-dual aged RAF of 2.341. It is billable for payment year 2026.
Coder answer: C77.4 is billable and maps to V28 HCC 18, Cancer Metastatic to Bone, Other and Unspecified Metastatic Cancer; Acute Leukemia Except Myeloid. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.
- Code
- C77.4
- Description
- Secondary and unspecified malignant neoplasm of inguinal and lower limb lymph nodes
- HCC (V28)
- HCC 18 — Cancer Metastatic to Bone, Other and Unspecified Metastatic Cancer; Acute Leukemia Except Myeloid
- RAF
- 2.341
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
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 C77.4 in the Code Book — tabular path, V28 RAF, and MEAT checklist →
MEAT Criteria for C77.4
For C77.4 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 C77.4 during that encounter, not just copy-forwarded from a problem list.
Coder workflow notes
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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 Cancer Metastatic to Bone, Other and Unspecified Metastatic Cancer; Acute Leukemia Except Myeloid (HCC 18) with a community, non-dual, aged base RAF weight of 2.341. 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 2.659. 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.
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