C84.A0 ICD-10-CM Code: Cutaneous T-cell lymphoma, unspecified, unspecified site
C84.A0 maps to CMS-HCC V28 20. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · HCC coding software
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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 guidanceCutaneous 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
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.
CMS-HCC V28
MappedHCC 20
Coefficient HCC 20: 1.136 (Community Non-Dual Aged (CNA))
CMS-HCC V24
HistoricalHistorical
Not used for CY2026 payment
ACA/HHS
MappedHCC 010
Code-level coefficient reference
ESRD/PACE
MappedHCC 10
Code-level coefficient reference
RXHCC
MappedHCC 21
Code-level coefficient reference
Code Book Path
Inclusion Terms
OfficialNo inclusion terms are included in this display for C84.A0. Check the code and parent instructions in the Code Book.
Excludes 2
Official- Kaposi's sarcoma of lymph nodes (C46.3)Inherited from C81-C96
- secondary and unspecified neoplasm of lymph nodes (C77.-)Inherited from C81-C96
- secondary neoplasm of bone marrow (C79.52)Inherited from C81-C96
- secondary neoplasm of spleen (C78.89)Inherited from C81-C96
Related Codes
Includes
OfficialNo Includes notes are included in this display for C84.A0. Check the code and parent instructions in the Code Book.
Excludes 1
Official- personal history of non-Hodgkin lymphoma (Z85.72)Inherited from C84
Code First
OfficialNo Code First sequencing instructions are included in this display for C84.A0. Check the code and parent instructions in the Code Book.
Use Additional
OfficialNo Use Additional Code instructions are included in this display for C84.A0. Check the code and parent instructions in the Code Book.
Code Also
OfficialNo Code Also instructions are included in this display for C84.A0. Check the code and parent instructions in the Code Book.
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 C84.A0 an HCC code?
Yes. C84.A0 (Cutaneous T-cell lymphoma, unspecified, unspecified site) maps to HCC 20, Lung and Other Severe Cancers under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 1.136. 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: C84.A0 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.A0
- Description
- Cutaneous T-cell lymphoma, unspecified, unspecified site
- HCC (V28)
- HCC 20 — Lung and Other Severe Cancers
- RAF reference coefficient
- 1.136
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
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 C84.A0 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →
MEAT review for C84.A0
For C84.A0, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.
- 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
Coder workflow notes
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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 source-labeled community, non-dual, aged reference coefficient of 1.136. No V24 mapping is shown for C84.A0; use the applicable model and payment year when reviewing the V28 mapping. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. 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.
Use C84.A0 when the provider wording supports cutaneous T-cell lymphoma, unspecified, unspecified site. Check the FY2026 tabular notes and the full code path before the final code choice. For C84.A0, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. 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 C84.A0 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Use C84.A0 when the provider wording supports cutaneous T-cell lymphoma, unspecified, unspecified site. 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, unspecified site. Keep the checklist tied to the note.
- •Do not swap C84.A0 with C84.A1. The FY2026 tabular describes C84.A1 as cutaneous T-cell lymphoma, unspecified lymph nodes of head, face, and neck. Follow the documented detail.
- •C84.A0 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.A0 or compare its code path with C84.A1.
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