What is ICD-10 code C84.A1?

C84.A1 is the ICD-10-CM diagnosis code for Cutaneous T-cell lymphoma, unspecified lymph nodes of head, face, and neck. A cancer of T cells that primarily affects the skin with involvement of lymph nodes in the head, face, and neck region. C84.A1 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C84.A1 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. C84.A1 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. C84.A1 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 C84.A1?

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 C84.A1, V28 maps to Lung and Other Severe Cancers at RAF 1.136 while V24 mapped to Lymphoma and Other Cancers at RAF 0.675. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting C84.A1?

Use C84.A1 when the provider wording supports cutaneous t-cell lymphoma, unspecified lymph nodes of head, face, and neck. Check the FY2026 tabular notes and the full code path before the final code choice. For this DOS, capture the provider's current assessment and the care action documented for cutaneous t-cell lymphoma, unspecified lymph nodes of head, face, and neck. Keep the checklist tied to the note. Do not swap C84.A1 with C84.A0. The FY2026 tabular describes C84.A0 as cutaneous t-cell lymphoma, unspecified, unspecified site. Follow the documented detail. Because C84.A1 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.

2026 ICD-10-CM C84.A1: Cutaneous T-cell lymphoma

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Code lookupC84.A1Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of lymphoid, hematopoietic and related tissue (C81-C96)

C84.A1

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

Cutaneous T-cell lymphoma, unspecified lymph nodes of head, face, and neck

A cancer of T cells that primarily affects the skin with involvement of lymph nodes in the head, face, and neck region.

Buddy Insight

Cutaneous T-cell lymphoma, unspecified, involving head, face, and neck lymph nodes indicates a skin-based T-cell lymphoma with nodal progression to the cervicofacial region.

CMS-HCC V28

Mapped

HCC 20

Lung and Other Severe Cancers

RAF 1.136

CMS-HCC V24

Mapped

HCC 10

Lymphoma and Other Cancers

RAF 0.675

ACA/HHS

Mapped

HCC 10

HHS-HCC 10

Varies by metal level

ESRD/PACE

Mapped

HCC 10

Lymphoma and Other Cancers

RAF 0.111

RXHCC

Mapped

HCC 21

Hodgkin Lymphoma and Other Ca...

RAF 0.410

Code Book Path

Official

C84Mature T/NK-cell lymphomas

C84.ACutaneous T-cell lymphoma, unspecified

C84.A1Cutaneous T-cell lymphoma, unspecified lymph nodes of head, face, and neck

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for C84.A1 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C84.A1 in this effective period.

Related Child Codes

Official

C84.A0Cutaneous T-cell lymphoma, unspecified, unspecified site

C84.A2Cutaneous T-cell lymphoma, unspecified, intrathoracic lymph nodes

C84.A3Cutaneous T-cell lymphoma, unspecified, intra-abdominal lymph nodes

C84.A4Cutaneous T-cell lymphoma, unspecified, lymph nodes of axilla and upper limb

C84.A5Cutaneous T-cell lymphoma, unspecified, lymph nodes of inguinal region and lower limb

Includes

Official

ICD-10-CM does not list Includes notes for C84.A1 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for C84.A1 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C84.A1 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C84.A1 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C84.A1 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Skin biopsy confirming cutaneous T-cell lymphoma

Physical exam or imaging documenting head, face, or neck lymph node involvement

Node biopsy or imaging confirming lymphomatous involvement (vs. reactive dermatopathic lymphadenopathy)

TNMB staging incorporating nodal findings

MEAT Support

HCC Buddy guidance

Skin biopsy confirming cutaneous T-cell lymphoma

Physical exam or imaging documenting head, face, or neck lymph node involvement

Node biopsy or imaging confirming lymphomatous involvement (vs. reactive dermatopathic lymphadenopathy)

TNMB staging incorporating nodal findings

Audit Caution

HCC Buddy guidance

Not distinguishing dermatopathic lymphadenopathy (reactive) from lymphomatous nodal involvement in CTCL patients

Using specific mycosis fungoides codes when the cutaneous subtype is actually unspecified

Confusing nodal progression of cutaneous lymphoma with primary nodal T-cell lymphoma

Failing to recognize that lymph node involvement upstages cutaneous T-cell lymphoma

Common Mistakes

HCC Buddy guidance

C84.01 — Mycosis fungoides, head/face/neck lymph nodes: If mycosis fungoides is specifically diagnosed

C84.91 — Mature T/NK-cell lymphoma, unspecified, head/face/neck: General T/NK lymphoma without cutaneous specification

C84.41 — PTCL-NOS, head/face/neck: Nodal T-cell lymphoma, not cutaneous primary

C77.0 — Secondary malignant neoplasm, head/face/neck lymph nodes: Metastatic disease, not primary lymphoma

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 C84.A1 an HCC code?

Yes. C84.A1 (Cutaneous T-cell lymphoma, unspecified lymph nodes of head, face, and neck) maps to Lung and Other Severe Cancers under the CMS-HCC V28 risk adjustment model (and Lymphoma and Other Cancers under V24), with a community non-dual aged RAF of 1.136. It is billable for payment year 2026.

Coder answer: C84.A1 is billable and maps to V28 HCC 20, Lung and Other Severe Cancers. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: C84.A1
Description: Cutaneous T-cell lymphoma, unspecified lymph nodes of head, face, and neck
HCC (V28): HCC 20 — Lung and Other Severe Cancers
RAF: 1.136
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 20, Lung and Other Severe Cancers

1.136

V24HCC 10, Lymphoma and Other Cancers

0.675

ESRDHCC 10, Lymphoma and Other Cancers

0.111

RxHCCHCC 21, Hodgkin Lymphoma and Other Cancers

0.410

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 C84.A1 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for C84.A1

For C84.A1 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 C84.A1 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

C84.A1 is the ICD-10-CM diagnosis code for cutaneous t-cell lymphoma, unspecified lymph nodes of head, face, and neck. A cancer of T cells that primarily affects the skin with involvement of lymph nodes in the head, face, and neck region. C84.A1 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of lymphoid, hematopoietic and related tissue (c81-c96).

Under the CMS-HCC V28 risk adjustment model, C84.A1 maps to Lung and Other Severe Cancers (HCC 20) with a community, non-dual, aged base RAF weight of 1.136. Under the older CMS-HCC V24 model, C84.A1 maps to Lymphoma and Other Cancers (HCC 10) with a community, non-dual, aged base RAF weight of 0.675. 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.

Use C84.A1 when the provider wording supports cutaneous t-cell lymphoma, unspecified lymph nodes of head, face, and neck. Check the FY2026 tabular notes and the full code path before the final code choice. Because C84.A1 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 C84.A1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Use C84.A1 when the provider wording supports cutaneous t-cell lymphoma, unspecified lymph nodes of head, face, and neck. Check the FY2026 tabular notes and the full code path before the final code choice.
•For this DOS, capture the provider's current assessment and the care action documented for cutaneous t-cell lymphoma, unspecified lymph nodes of head, face, and neck. Keep the checklist tied to the note.
•Do not swap C84.A1 with C84.A0. The FY2026 tabular describes C84.A0 as cutaneous t-cell lymphoma, unspecified, unspecified site. Follow the documented detail.
•C84.A1 maps to V28 HCC 20, Lung and Other Severe Cancers. The mapping does not replace the documentation review. The code still has to match the note.
•Ask Buddy to show the official notes for C84.A1 or compare its code path with C84.A0.

Clinical Significance

Cutaneous T-cell lymphoma, unspecified, involving head, face, and neck lymph nodes indicates a skin-based T-cell lymphoma with nodal progression to the cervicofacial region. Lymph node involvement in cutaneous T-cell lymphoma represents disease advancement beyond the skin and significantly impacts staging and prognosis. Head and neck nodes may be palpable on examination.

Documentation Requirements

✓Skin biopsy confirming cutaneous T-cell lymphoma
✓Physical exam or imaging documenting head, face, or neck lymph node involvement
✓Node biopsy or imaging confirming lymphomatous involvement (vs. reactive dermatopathic lymphadenopathy)
✓TNMB staging incorporating nodal findings
✓Explanation if specific CTCL subtype cannot be determined

Commonly Confused Codes

•C84.01: Mycosis fungoides, head/face/neck lymph nodes: If mycosis fungoides is specifically diagnosed
•C84.91: Mature T/NK-cell lymphoma, unspecified, head/face/neck: General T/NK lymphoma without cutaneous specification
•C84.41: PTCL-NOS, head/face/neck: Nodal T-cell lymphoma, not cutaneous primary
•C77.0: Secondary malignant neoplasm, head/face/neck lymph nodes: Metastatic disease, not primary lymphoma