What is ICD-10 code C10.4?

C10.4 is the ICD-10-CM diagnosis code for Malignant neoplasm of branchial cleft. Cancer arising from a branchial cleft, which is a remnant of embryonic tissue in the neck that can develop into a cyst or tumor. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C10.4 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C10.4 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. C10.4 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. C10.4 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.

Which HCC does C10.4 map to under V28?

C10.4 maps to CMS-HCC V28 HCC 21 (Lymphoma and Other Cancers). The category numbers, labels, and conditions come from the CMS-HCC V28 model file for payment year 2026.

What documentation supports C10.4?

Branchial cleft cancers are rare and typically arise from branchial cleft cysts that have undergone malignant transformation Verify that pathology confirms malignancy arising from branchial cleft tissue rather than primary oropharyngeal cancer Because C10.4 maps to an HCC category, the documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) before the diagnosis is used for risk adjustment. 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 C10.4: Malignant neoplasm

C10.4 maps to CMS-HCC V28 21. A source-labeled RAF reference is available. Documentation must support MEAT. MEAT criteria · RAF Calculator · HCC coding software

ICD-10-CM Code View

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Code lookupC10.4Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of lip, oral cavity and pharynx (C00-C14)

C10.4

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

Malignant neoplasm of branchial cleft

Cancer arising from a branchial cleft, which is a remnant of embryonic tissue in the neck that can develop into a cyst or tumor.

Buddy Insight

Malignant neoplasm of the branchial cleft is a rare tumor arising from embryonic remnant tissue in the neck.

CMS-HCC V28

Mapped

HCC 21

Lymphoma and Other Cancers

Code-level coefficient reference

CMS-HCC V24

Historical

Not used for standard CY2026 Medicare Advantage payment. Select a historical period to review V24.

Not used for CY2026 payment

ACA/HHS

Mapped

HCC 011

HHS-HCC 011 adult, RAF varies...

Code-level coefficient reference

ESRD/PACE

Mapped

HCC 11

Colorectal/Bladder/and Other ...

Code-level coefficient reference

RXHCC

N/A

—

Not risk-adjusted for this model/period.

Not mapped

Code Book Path

Official

C10Malignant neoplasm of oropharynx

C10.4Malignant neoplasm of branchial cleft

Inclusion Terms

Official

Malignant neoplasm of branchial cyst [site of neoplasm]

Excludes 2

Official

malignant neoplasm of tonsil (C09.-)

Related Child Codes

Official

C10.0Malignant neoplasm of vallecula

C10.1Malignant neoplasm of anterior surface of epiglottis

C10.2Malignant neoplasm of lateral wall of oropharynx

C10.3Malignant neoplasm of posterior wall of oropharynx

C10.8Malignant neoplasm of overlapping sites of oropharynx

Includes

Official

ICD-10-CM does not list Includes notes for C10.4 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for C10.4 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C10.4 in this effective period.

Use Additional

Official

code to identify:
alcohol abuse and dependence (F10.-)
exposure to environmental tobacco smoke (Z77.22)
exposure to tobacco smoke in the perinatal period (P96.81)
history of tobacco dependence (Z87.891)

Code Also

Official

ICD-10-CM does not list Code Also instructions for C10.4 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Pathology confirming malignancy arising from branchial cleft tissue

Exclusion of occult primary oropharyngeal cancer (particularly HPV-related tonsillar or tongue base cancer)

HPV/p16 testing of the tumor specimen

Documentation of complete head and neck evaluation including PET/CT or MRI to rule out other primary sites

MEAT Support

HCC Buddy guidance

Pathology confirming malignancy arising from branchial cleft tissue

Exclusion of occult primary oropharyngeal cancer (particularly HPV-related tonsillar or tongue base cancer)

HPV/p16 testing of the tumor specimen

Documentation of complete head and neck evaluation including PET/CT or MRI to rule out other primary sites

Audit Caution

HCC Buddy guidance

Accepting a branchial cleft carcinoma diagnosis without documentation of workup to exclude occult oropharyngeal primary

Not checking HPV/p16 status — HPV-positive cystic neck nodes from occult tonsillar cancer are frequently misdiagnosed as branchial cleft carcinoma

Coding benign branchial cleft cysts with this malignant neoplasm code

Failing to document the comprehensive head and neck evaluation required to support this diagnosis

Common Mistakes

HCC Buddy guidance

C77.0 — Secondary malignant neoplasm of lymph nodes of head, face, and neck; cystic metastatic disease may mimic branchial cleft carcinoma

C09.0 — Tonsillar fossa; many apparent branchial cleft carcinomas are actually cystic metastases from tonsillar primaries

D18.1 — Lymphangioma; benign branchial cleft cysts are not coded here

C10.9 — Oropharynx, unspecified; occult oropharyngeal primary may present as a neck mass

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 C10.4 an HCC code?

Yes. C10.4 (Malignant neoplasm of branchial cleft) maps to HCC 21, Lymphoma and Other Cancers under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.671. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.

Coder answer: C10.4 is billable and maps to V28 HCC 21, Lymphoma and Other Cancers. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: C10.4
Description: Malignant neoplasm of branchial cleft
HCC (V28): HCC 21 — Lymphoma and Other Cancers
RAF reference coefficient: 0.671
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 21, Lymphoma and Other Cancers

0.671

ESRDHCC 11, Colorectal/Bladder/and Other Cancers

Not separately weighted

These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. 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 context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.

Work C10.4 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT Criteria for C10.4

For C10.4 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 C10.4 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

C10.4 is the ICD-10-CM diagnosis code for malignant neoplasm of branchial cleft. Cancer arising from a branchial cleft, which is a remnant of embryonic tissue in the neck that can develop into a cyst or tumor. C10.4 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of lip, oral cavity and pharynx (c00-c14).

Under the CMS-HCC V28 risk adjustment model, C10.4 maps to Lymphoma and Other Cancers (HCC 21) with a source-labeled community, non-dual, aged reference coefficient of 0.671. No V24 mapping is shown for C10.4; use the applicable model and payment year when reviewing the V28 mapping. 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. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.

Branchial cleft cancers are rare and typically arise from branchial cleft cysts that have undergone malignant transformation. Because C10.4 maps to an HCC category, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) before the diagnosis is used for risk adjustment. 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, source-labeled coefficient references, and MEAT documentation criteria for C10.4 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Branchial cleft cancers are rare and typically arise from branchial cleft cysts that have undergone malignant transformation
•Verify that pathology confirms malignancy arising from branchial cleft tissue rather than primary oropharyngeal cancer

Clinical Significance

Malignant neoplasm of the branchial cleft is a rare tumor arising from embryonic remnant tissue in the neck. Branchial cleft carcinomas are controversial in oncology — some experts question whether primary branchial cleft carcinomas exist at all, arguing that most represent cystic metastases from occult oropharyngeal primaries, particularly HPV-related tumors.

Documentation Requirements

✓Pathology confirming malignancy arising from branchial cleft tissue
✓Exclusion of occult primary oropharyngeal cancer (particularly HPV-related tonsillar or tongue base cancer)
✓HPV/p16 testing of the tumor specimen
✓Documentation of complete head and neck evaluation including PET/CT or MRI to rule out other primary sites
✓Laterality and relationship to sternocleidomastoid muscle and great vessels

Commonly Confused Codes

•C77.0: Secondary malignant neoplasm of lymph nodes of head, face, and neck; cystic metastatic disease may mimic branchial cleft carcinoma
•C09.0: Tonsillar fossa; many apparent branchial cleft carcinomas are actually cystic metastases from tonsillar primaries
•D18.1: Lymphangioma; benign branchial cleft cysts are not coded here
•C10.9: Oropharynx, unspecified; occult oropharyngeal primary may present as a neck mass