What is ICD-10 code C84.42?

C84.42 is the ICD-10-CM diagnosis code for Peripheral T-cell lymphoma, not elsewhere classified, intrathoracic lymph nodes. A type of T-cell lymphoma affecting the lymph nodes inside the chest cavity. It belongs to the ICD-10-CM chapter for neoplasms (c00-d49). C84.42 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. C84.42 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. C84.42 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. C84.42 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 C84.42?

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 C84.42, V28 maps to Lymphoma and Other Cancers at RAF 0.105 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 C84.42?

Verify documentation confirms intrathoracic (within the chest) lymph node involvement This includes mediastinal and hilar lymph nodes Because C84.42 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.

C84.42 ICD-10 Code: Peripheral 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 lookupC84.42Effective periodFY2026 Apr Update (Apr 1-Sep 30)

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

C84.42

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

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

A type of T-cell lymphoma affecting the lymph nodes inside the chest cavity.

Buddy Insight

Peripheral T-cell lymphoma not elsewhere classified involving intrathoracic lymph nodes represents an aggressive non-Hodgkin lymphoma subtype with poor prognosis.

CMS-HCC V28

Mapped

HCC 19

Lymphoma and Other Cancers

RAF 0.105

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

Basket needed

Compare selected patient codes to show trumped or trumps impact.

Code Book Path

Official

C84Mature T/NK-cell lymphomas

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

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

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 C84.42 in this effective period.

Related Child Codes

Official

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

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

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 C84.42 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for C84.42 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for C84.42 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for C84.42 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for C84.42 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Pathology report confirming peripheral T-cell lymphoma, NOS (not a more specific T-cell lymphoma subtype)

Imaging (CT or PET/CT) documenting intrathoracic lymph node involvement (mediastinal, hilar, or paratracheal nodes)

Immunohistochemistry panel showing T-cell markers (CD3+, CD4+ or CD8+) and excluding other specific T-cell lymphoma subtypes

Current treatment status and clinical stage (Ann Arbor staging system)

MEAT Support

HCC Buddy guidance

Pathology report confirming peripheral T-cell lymphoma, NOS (not a more specific T-cell lymphoma subtype)

Imaging (CT or PET/CT) documenting intrathoracic lymph node involvement (mediastinal, hilar, or paratracheal nodes)

Immunohistochemistry panel showing T-cell markers (CD3+, CD4+ or CD8+) and excluding other specific T-cell lymphoma subtypes

Current treatment status and clinical stage (Ann Arbor staging system)

Audit Caution

HCC Buddy guidance

Assigning PTCL-NOS when a more specific T-cell lymphoma subtype (angioimmunoblastic, anaplastic large cell, hepatosplenic) is documented in pathology

Using unspecified site code C84.40 when imaging clearly identifies intrathoracic involvement

Failing to verify the pathology confirms T-cell lineage rather than B-cell or NK-cell origin

Not updating the code when disease progresses to multiple sites (should change to C84.48) or enters remission (should change to C84.4A)

Common Mistakes

HCC Buddy guidance

C84.62 — Anaplastic large cell lymphoma, ALK-positive, intrathoracic lymph nodes: ALCL is a specific subtype with distinct morphology (hallmark cells) and ALK expression; PTCL-NOS is a diagnosis of exclusion when no specific T-cell lymphoma subtype fits

C84.72 — Anaplastic large cell lymphoma, ALK-negative, intrathoracic lymph nodes: ALK-negative ALCL has specific morphologic features distinguishing it from PTCL-NOS

C85.12 — Unspecified B-cell lymphoma, intrathoracic lymph nodes: B-cell lineage must be excluded through immunophenotyping before assigning a T-cell lymphoma code

C84.48 — PTCL-NOS, lymph nodes of multiple sites: Use C84.42 only when involvement is limited to intrathoracic nodes; if other regions are also involved, C84.48 is appropriate

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 C84.42 an HCC code?

Yes. C84.42 maps to Lymphoma and Other Cancers under the CMS-HCC V28 risk adjustment model (and Lymphoma and Other Cancers under V24).

HCC Category Mapping

V28HCC 19, Lymphoma and Other Cancers

0.105

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 C84.42

For C84.42to 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 C84.42 during that encounter, not just copy-forwarded from a problem list.

What This Code Means

C84.42 is the ICD-10-CM diagnosis code for peripheral t-cell lymphoma, not elsewhere classified, intrathoracic lymph nodes. A type of T-cell lymphoma affecting the lymph nodes inside the chest cavity. C84.42 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, C84.42 maps to Lymphoma and Other Cancers (HCC 19) with a community, non-dual, aged base RAF weight of 0.105. Under the older V24 model, C84.42 mapped to the same category but with a base RAF weight of 0.675, V28 recalibrated weights across the entire model. 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.

Verify documentation confirms intrathoracic (within the chest) lymph node involvement. Because C84.42 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 C84.42 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Verify documentation confirms intrathoracic (within the chest) lymph node involvement
•This includes mediastinal and hilar lymph nodes

Clinical Significance

Peripheral T-cell lymphoma not elsewhere classified involving intrathoracic lymph nodes represents an aggressive non-Hodgkin lymphoma subtype with poor prognosis. Site-specific coding is critical because intrathoracic involvement may indicate mediastinal bulky disease, which affects staging and treatment approach. Accurate capture ensures appropriate resource allocation for this high-acuity malignancy.

Documentation Requirements

✓Pathology report confirming peripheral T-cell lymphoma, NOS (not a more specific T-cell lymphoma subtype)
✓Imaging (CT or PET/CT) documenting intrathoracic lymph node involvement (mediastinal, hilar, or paratracheal nodes)
✓Immunohistochemistry panel showing T-cell markers (CD3+, CD4+ or CD8+) and excluding other specific T-cell lymphoma subtypes
✓Current treatment status and clinical stage (Ann Arbor staging system)
✓Documentation that this is active disease, not in remission

Commonly Confused Codes

•C84.62 — Anaplastic large cell lymphoma, ALK-positive, intrathoracic lymph nodes: ALCL is a specific subtype with distinct morphology (hallmark cells) and ALK expression; PTCL-NOS is a diagnosis of exclusion when no specific T-cell lymphoma subtype fits
•C84.72 — Anaplastic large cell lymphoma, ALK-negative, intrathoracic lymph nodes: ALK-negative ALCL has specific morphologic features distinguishing it from PTCL-NOS
•C85.12 — Unspecified B-cell lymphoma, intrathoracic lymph nodes: B-cell lineage must be excluded through immunophenotyping before assigning a T-cell lymphoma code
•C84.48 — PTCL-NOS, lymph nodes of multiple sites: Use C84.42 only when involvement is limited to intrathoracic nodes; if other regions are also involved, C84.48 is appropriate