What is ICD-10 code C84.02?

C84.02 is the ICD-10-CM diagnosis code for Mycosis fungoides, intrathoracic lymph nodes. A rare type of skin cancer (mycosis fungoides) that has spread to the lymph nodes inside the chest. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C84.02 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C84.02 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. C84.02 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. C84.02 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 C84.02 map to under V28?

C84.02 maps to CMS-HCC V28 HCC 20 (Lung and Other Severe Cancers). The category numbers, labels, and conditions come from the CMS-HCC V28 model file for payment year 2026.

2026 ICD-10-CM C84.02: Mycosis fungoides

C84.02 maps to CMS-HCC V28 20. A source-labeled RAF reference is available. Documentation must support MEAT. MEAT criteria · RAF Calculator · HCC coding software

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Code lookupC84.02Effective periodFY2026 Apr Update (Apr 1-Sep 30)

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

C84.02

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

Mycosis fungoides, intrathoracic lymph nodes

A rare type of skin cancer (mycosis fungoides) that has spread to the lymph nodes inside the chest.

Buddy Insight

Mycosis fungoides with intrathoracic lymph node involvement indicates advanced disease with spread to mediastinal or hilar lymph nodes.

CMS-HCC V28

Mapped

HCC 20

Lung and Other Severe 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 010

HHS-HCC 010 adult, RAF varies...

Code-level coefficient reference

ESRD/PACE

Mapped

HCC 10

Lymphoma and Other Cancers

Code-level coefficient reference

RXHCC

Mapped

HCC 19

Leukemias and Other Hematolog...

Code-level coefficient reference

Code Book Path

Official

C84Mature T/NK-cell lymphomas

C84.0Mycosis fungoides

C84.02Mycosis fungoides, intrathoracic lymph nodes

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for C84.02 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C84.02 in this effective period.

Related Child Codes

Official

C84.00Mycosis fungoides, unspecified site

C84.01Mycosis fungoides, lymph nodes of head, face, and neck

C84.03Mycosis fungoides, intra-abdominal lymph nodes

C84.04Mycosis fungoides, lymph nodes of axilla and upper limb

C84.05Mycosis fungoides, lymph nodes of inguinal region and lower limb

Includes

Official

ICD-10-CM does not list Includes notes for C84.02 in this effective period.

Excludes 1

Official

peripheral T-cell lymphoma, not elsewhere classified (C84.4-)

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C84.02 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C84.02 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C84.02 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Skin biopsy confirming mycosis fungoides diagnosis

Chest imaging (CT or PET/CT) documenting intrathoracic lymphadenopathy

Pathologic confirmation of lymphomatous involvement if biopsy performed

TNMB staging reflecting intrathoracic nodal disease

MEAT Support

HCC Buddy guidance

Skin biopsy confirming mycosis fungoides diagnosis

Chest imaging (CT or PET/CT) documenting intrathoracic lymphadenopathy

Pathologic confirmation of lymphomatous involvement if biopsy performed

TNMB staging reflecting intrathoracic nodal disease

Audit Caution

HCC Buddy guidance

Not recognizing that intrathoracic lymph node involvement represents advanced mycosis fungoides requiring different staging and treatment

Using unspecified site when staging CT clearly shows mediastinal or hilar lymphadenopathy

Failing to distinguish between reactive lymphadenopathy and pathologic involvement on staging scans

Confusing intrathoracic nodal disease with pulmonary parenchymal involvement (which would be extranodal)

Common Mistakes

HCC Buddy guidance

C84.00 — Mycosis fungoides, unspecified site: Use C84.02 when intrathoracic lymph node involvement is confirmed

C84.12 — Sezary disease, intrathoracic: Distinct diagnosis; Sezary disease requires circulating malignant T-cells

C83.92 — Non-follicular lymphoma, unspecified, intrathoracic: Use for non-follicular lymphoma, not mycosis fungoides

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 C84.02 an HCC code?

Yes. C84.02 (Mycosis fungoides, intrathoracic lymph nodes) 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: C84.02 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: C84.02
Description: Mycosis fungoides, intrathoracic lymph nodes
HCC (V28): HCC 20 — Lung and Other Severe Cancers
RAF reference coefficient: 1.136
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 20, Lung and Other Severe Cancers

1.136

ESRDHCC 10, Lymphoma and Other Cancers

Not separately weighted

RxHCCHCC 19, Leukemias and Other Hematologic 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 C84.02 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT Criteria for C84.02

For C84.02 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 C84.02 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

C84.02 is the ICD-10-CM diagnosis code for mycosis fungoides, intrathoracic lymph nodes. A rare type of skin cancer (mycosis fungoides) that has spread to the lymph nodes inside the chest. C84.02 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, C84.02 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 C84.02; 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.

Confirm intrathoracic lymph node involvement through CT chest imaging. Because C84.02 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 C84.02 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Confirm intrathoracic lymph node involvement through CT chest imaging
•The '2' designator indicates mediastinal and hilar lymph node involvement

Clinical Significance

Mycosis fungoides with intrathoracic lymph node involvement indicates advanced disease with spread to mediastinal or hilar lymph nodes. This is uncommon in mycosis fungoides and represents significant disease progression requiring systemic treatment. Intrathoracic involvement is typically detected on staging CT or PET/CT scans.

Documentation Requirements

✓Skin biopsy confirming mycosis fungoides diagnosis
✓Chest imaging (CT or PET/CT) documenting intrathoracic lymphadenopathy
✓Pathologic confirmation of lymphomatous involvement if biopsy performed
✓TNMB staging reflecting intrathoracic nodal disease
✓Systemic treatment plan

Commonly Confused Codes

•C84.00: Mycosis fungoides, unspecified site: Use C84.02 when intrathoracic lymph node involvement is confirmed
•C84.12: Sezary disease, intrathoracic: Distinct diagnosis; Sezary disease requires circulating malignant T-cells
•C83.92: Non-follicular lymphoma, unspecified, intrathoracic: Use for non-follicular lymphoma, not mycosis fungoides