C84.42
BillablePeripheral T-cell lymphoma, not elsewhere classified, intrathoracic lymph nodes
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
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
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 C84.42 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 C84.42 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