C84.03
BillableMycosis fungoides, intra-abdominal lymph nodes
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is C84.03 an HCC code?
Yes. C84.03 maps to Lung and Other Severe 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 C84.03
For C84.03 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 C84.03 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
C84.03 is the ICD-10-CM diagnosis code for mycosis fungoides, intra-abdominal lymph nodes. Mycosis fungoides is a type of blood cancer that starts in skin T-cells and has spread to the lymph nodes inside the abdomen. This is an advanced stage of the disease where cancer cells are found in the abdominal lymph node region. C84.03 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, C84.03 maps to Lung and Other Severe Cancers (HCC 20) with a community, non-dual, aged base RAF weight of 0.000. Under the older CMS-HCC V24 model, C84.03 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.
Verify documentation specifies the lymph node location as intra-abdominal; if lymph nodes are in other locations (peripheral, mediastinal, etc.), use different C84.0x subcodes. Because C84.03 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 C84.03 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Verify documentation specifies the lymph node location as intra-abdominal; if lymph nodes are in other locations (peripheral, mediastinal, etc.), use different C84.0x subcodes
- •Mycosis fungoides requires staging information; ensure the stage is documented and coded separately if applicable, as this code alone does not capture disease stage
Clinical Significance
Mycosis fungoides with intra-abdominal lymph node involvement indicates significant disease progression with visceral lymph node spread. Abdominal lymph node involvement in mycosis fungoides is associated with advanced staging and poor prognosis, requiring aggressive systemic therapy. This presentation is uncommon and represents transformation from early-stage cutaneous disease.
Documentation Requirements
- ✓Skin biopsy confirming mycosis fungoides
- ✓Abdominal imaging (CT or PET/CT) documenting intra-abdominal lymphadenopathy
- ✓Pathologic confirmation of nodal involvement if biopsy obtained
- ✓TNMB staging reflecting visceral lymph node disease
- ✓Treatment plan addressing advanced-stage disease
Commonly Confused Codes
- •C84.09 — Mycosis fungoides, extranodal: Use when abdominal organs (not lymph nodes) are involved
- •C84.00 — Mycosis fungoides, unspecified site: Use C84.03 when intra-abdominal nodal disease is confirmed
- •C83.93 — Non-follicular lymphoma, unspecified, intra-abdominal: For non-follicular lymphoma, not mycosis fungoides