What is ICD-10 code C84.40?

C84.40 is the ICD-10-CM diagnosis code for Peripheral T-cell lymphoma, not elsewhere classified, unspecified site. A type of T-cell lymphoma (a blood cancer) that does not fit into other specific categories and affects an unspecified location in the body. C84.40 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C84.40 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. C84.40 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. C84.40 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 C84.40?

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 C84.40, V28 maps to Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers at RAF 1.798 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 C84.40?

Use this code only when the specific site of involvement is not documented or is unknown If a specific lymph node site is documented, use codes C84.41-C84.46 instead Because C84.40 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 C84.40: Peripheral T-cell lymphoma

ICD-10-CM Code View

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Code lookupC84.40Effective periodFY2026 Apr Update (Apr 1-Sep 30)

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

C84.40

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

Peripheral T-cell lymphoma, not elsewhere classified, unspecified site

A type of T-cell lymphoma (a blood cancer) that does not fit into other specific categories and affects an unspecified location in the body.

Buddy Insight

CMS-HCC V28

Mapped

HCC 19

Myelodysplastic Syndromes, Mu...

RAF 1.798

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

C84.4Peripheral T-cell lymphoma, not elsewhere classified

C84.40Peripheral T-cell lymphoma, not elsewhere classified, unspecified site

Inclusion Terms

Official

Lennert's lymphoma
Lymphoepithelioid lymphoma
Mature T-cell lymphoma, not elsewhere classified

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for C84.40 in this effective period.

Related Child Codes

Official

C84.41Peripheral T-cell lymphoma, not elsewhere classified, lymph nodes of head, face, and neck

C84.42Peripheral T-cell lymphoma, not elsewhere classified, intrathoracic lymph nodes

C84.43Peripheral T-cell lymphoma, not elsewhere classified, intra-abdominal lymph nodes

C84.44Peripheral T-cell lymphoma, not elsewhere classified, lymph nodes of axilla and upper limb

C84.45Peripheral T-cell lymphoma, not elsewhere classified, lymph nodes of inguinal region and lower limb

Includes

Official

ICD-10-CM does not list Includes notes for C84.40 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for C84.40 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C84.40 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C84.40 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C84.40 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Pathology confirming peripheral T-cell lymphoma with immunohistochemistry demonstrating T-cell markers

Exclusion of other specific T-cell lymphoma subtypes (mycosis fungoides, Sezary disease, anaplastic large cell lymphoma, etc.)

Staging documentation including imaging (CT or PET/CT)

Documentation of specific site if available — query provider if site not specified

MEAT Support

HCC Buddy guidance

Pathology confirming peripheral T-cell lymphoma with immunohistochemistry demonstrating T-cell markers

Exclusion of other specific T-cell lymphoma subtypes (mycosis fungoides, Sezary disease, anaplastic large cell lymphoma, etc.)

Staging documentation including imaging (CT or PET/CT)

Documentation of specific site if available — query provider if site not specified

Audit Caution

HCC Buddy guidance

Using this code when a more specific T-cell lymphoma subtype has been identified (angioimmunoblastic, anaplastic large cell, etc.)

Confusing peripheral T-cell lymphoma with peripheral nerve tumors or peripheral neuropathy — 'peripheral' refers to mature T-cells, not anatomic location

Not verifying T-cell lineage through immunohistochemistry before coding as T-cell lymphoma

Using this code for cutaneous T-cell lymphomas which have their own specific code categories

Common Mistakes

HCC Buddy guidance

C84.00 — Mycosis fungoides: A cutaneous T-cell lymphoma with distinct biology and treatment; peripheral T-cell lymphoma is a nodal/systemic disease

C84.10 — Sezary disease: A leukemic cutaneous T-cell lymphoma, distinct from peripheral T-cell lymphoma

C86.0-C86.6 — Other specified T-cell lymphomas: Specific entities like hepatosplenic T-cell lymphoma, subcutaneous panniculitis-like T-cell lymphoma have their own codes

C85.10 — Unspecified B-cell lymphoma: Verify T-cell vs. B-cell lineage on immunohistochemistry; treatment is fundamentally different

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 C84.40 an HCC code?

Yes. C84.40 (Peripheral T-cell lymphoma, not elsewhere classified, unspecified site) maps to Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers under the CMS-HCC V28 risk adjustment model (and Lymphoma and Other Cancers under V24), with a community non-dual aged RAF of 1.798. It is billable for payment year 2026.

Coder answer: C84.40 is billable and maps to V28 HCC 19, Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: C84.40
Description: Peripheral T-cell lymphoma, not elsewhere classified, unspecified site
HCC (V28): HCC 19 — Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers
RAF: 1.798
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 19, Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers

1.798

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 C84.40 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for C84.40

For C84.40 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 C84.40 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

C84.40 is the ICD-10-CM diagnosis code for peripheral t-cell lymphoma, not elsewhere classified, unspecified site. A type of T-cell lymphoma (a blood cancer) that does not fit into other specific categories and affects an unspecified location in the body. C84.40 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, C84.40 maps to Myelodysplastic Syndromes, Multiple Myeloma, and Other Cancers (HCC 19) with a community, non-dual, aged base RAF weight of 1.798. Under the older CMS-HCC V24 model, C84.40 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 this code only when the specific site of involvement is not documented or is unknown. Because C84.40 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 C84.40 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Use this code only when the specific site of involvement is not documented or is unknown
•If a specific lymph node site is documented, use codes C84.41-C84.46 instead

Clinical Significance

Peripheral T-cell lymphoma, not elsewhere classified, at an unspecified site is an aggressive non-Hodgkin lymphoma originating from mature T-cells that does not fit into other specific T-cell lymphoma categories. This is a heterogeneous group of lymphomas with generally poor prognosis and limited treatment options compared to B-cell lymphomas. Accurate identification is important because peripheral T-cell lymphomas require different treatment protocols than B-cell lymphomas.

Documentation Requirements

✓Pathology confirming peripheral T-cell lymphoma with immunohistochemistry demonstrating T-cell markers
✓Exclusion of other specific T-cell lymphoma subtypes (mycosis fungoides, Sezary disease, anaplastic large cell lymphoma, etc.)
✓Staging documentation including imaging (CT or PET/CT)
✓Documentation of specific site if available — query provider if site not specified
✓Treatment plan — typically anthracycline-based chemotherapy

Commonly Confused Codes

•C84.00: Mycosis fungoides: A cutaneous T-cell lymphoma with distinct biology and treatment; peripheral T-cell lymphoma is a nodal/systemic disease
•C84.10: Sezary disease: A leukemic cutaneous T-cell lymphoma, distinct from peripheral T-cell lymphoma
•C86.0-C86.6: Other specified T-cell lymphomas: Specific entities like hepatosplenic T-cell lymphoma, subcutaneous panniculitis-like T-cell lymphoma have their own codes
•C85.10: Unspecified B-cell lymphoma: Verify T-cell vs. B-cell lineage on immunohistochemistry; treatment is fundamentally different