What is ICD-10 code C84.A0?

C84.A0 is the ICD-10-CM diagnosis code for Cutaneous T-cell lymphoma, unspecified, unspecified site. A cancer of T cells that primarily affects the skin, but the specific location of affected lymph nodes is not specified. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C84.A0 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C84.A0 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.A0 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.A0 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.A0?

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.A0, V28 maps to Lung and Other Severe Cancers at RAF 0.000 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.A0?

This is the default code when cutaneous T-cell lymphoma is present but lymph node location is unknown or unspecified If lymph node involvement location is documented, use a more specific C84.A1-A7 code instead Because C84.A0 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.

C84.A0 ICD-10 Code: Cutaneous T-cell lymphoma

ICD-10-CM Code View

HCC Buddy Code Card

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

Code lookupC84.A0Effective 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.A0

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

Cutaneous T-cell lymphoma, unspecified, unspecified site

A cancer of T cells that primarily affects the skin, but the specific location of affected lymph nodes is not specified.

Buddy Insight

CMS-HCC V28

Mapped

HCC 20

Lung and Other Severe Cancers

RAF 0.0

CMS-HCC V24

Mapped

HCC 10

Lymphoma and Other Cancers

RAF 0.675

ACA/HHS

Not risk-adjusted for this model/period.

RAF 0

ESRD/PACE

Mapped

HCC 10

Lymphoma and Other Cancers

RAF 0.0

RXHCC

Mapped

HCC 21

Hodgkin Lymphoma and Other Ca...

RAF 0.0

Code Trumping

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Compare selected patient codes to show trumped or trumps impact.

Code Book Path

Official

C84Mature T/NK-cell lymphomas

C84.ACutaneous T-cell lymphoma, unspecified

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

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for C84.A0 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C84.A0 in this effective period.

Related Child Codes

Official

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

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.A0 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for C84.A0 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C84.A0 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C84.A0 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C84.A0 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Skin biopsy confirming T-cell lymphoma with cutaneous tropism

Immunophenotyping showing T-cell markers with skin involvement pattern

Documentation explaining why specific subtype (mycosis fungoides, Sezary syndrome) cannot be determined

Skin examination findings (patches, plaques, tumors, erythroderma)

MEAT Support

HCC Buddy guidance

Skin biopsy confirming T-cell lymphoma with cutaneous tropism

Immunophenotyping showing T-cell markers with skin involvement pattern

Documentation explaining why specific subtype (mycosis fungoides, Sezary syndrome) cannot be determined

Skin examination findings (patches, plaques, tumors, erythroderma)

Audit Caution

HCC Buddy guidance

Using this code when mycosis fungoides or Sezary syndrome is specifically diagnosed — use their dedicated codes

Confusing cutaneous T-cell lymphoma with primary cutaneous B-cell lymphoma (C86 series)

Not distinguishing cutaneous T-cell lymphoma from reactive skin conditions that can mimic it clinically

Failing to stage using the TNMB system specific to cutaneous lymphomas rather than Ann Arbor staging

Common Mistakes

HCC Buddy guidance

C84.00 — Mycosis fungoides, unspecified site: The most common cutaneous T-cell lymphoma; use when specifically diagnosed

C84.10 — Sezary syndrome: Leukemic variant of cutaneous T-cell lymphoma with erythroderma and circulating Sezary cells

C84.90 — Mature T/NK-cell lymphoma, unspecified: General T/NK lymphoma code without cutaneous specification

L41.0 — Pityriasis lichenoides et varioliformis acuta: Reactive skin condition that can mimic cutaneous T-cell lymphoma

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 C84.A0 an HCC code?

Yes. C84.A0 maps to Lung and Other Severe Cancers under the CMS-HCC V28 risk adjustment model (and Lymphoma and Other Cancers under V24).

HCC Category Mapping

V28HCC 20, Lung and Other Severe Cancers

0.000

V24HCC 10, Lymphoma and Other Cancers

0.675

ESRDHCC 10, Lymphoma and Other Cancers

0.000

RxHCCHCC 21, Hodgkin Lymphoma and Other Cancers

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 C84.A0

For C84.A0to 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.A0 during that encounter, not just copy-forwarded from a problem list.

What This Code Means

C84.A0 is the ICD-10-CM diagnosis code for cutaneous t-cell lymphoma, unspecified, unspecified site. A cancer of T cells that primarily affects the skin, but the specific location of affected lymph nodes is not specified. C84.A0 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.A0 maps to Lung and Other Severe Cancers (HCC 20) with a community, non-dual, aged base RAF weight of 0.000. Under the older CMS-HCC V24 model, C84.A0 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.

This is the default code when cutaneous T-cell lymphoma is present but lymph node location is unknown or unspecified. Because C84.A0 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.A0 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•This is the default code when cutaneous T-cell lymphoma is present but lymph node location is unknown or unspecified
•If lymph node involvement location is documented, use a more specific C84.A1-A7 code instead

Clinical Significance

Cutaneous T-cell lymphoma, unspecified, unspecified site is a general code for T-cell lymphomas that primarily involve the skin when neither the specific subtype (mycosis fungoides, Sezary syndrome, etc.) nor the lymph node involvement site is specified. Cutaneous T-cell lymphomas are a distinct group from nodal T-cell lymphomas, with different natural histories and treatment approaches. This code should prompt efforts to classify the specific cutaneous subtype.

Documentation Requirements

✓Skin biopsy confirming T-cell lymphoma with cutaneous tropism
✓Immunophenotyping showing T-cell markers with skin involvement pattern
✓Documentation explaining why specific subtype (mycosis fungoides, Sezary syndrome) cannot be determined
✓Skin examination findings (patches, plaques, tumors, erythroderma)
✓Staging using TNMB system specific to cutaneous lymphoma

Commonly Confused Codes

•C84.00 — Mycosis fungoides, unspecified site: The most common cutaneous T-cell lymphoma; use when specifically diagnosed
•C84.10 — Sezary syndrome: Leukemic variant of cutaneous T-cell lymphoma with erythroderma and circulating Sezary cells
•C84.90 — Mature T/NK-cell lymphoma, unspecified: General T/NK lymphoma code without cutaneous specification
•L41.0 — Pityriasis lichenoides et varioliformis acuta: Reactive skin condition that can mimic cutaneous T-cell lymphoma