C84.00
BillableMycosis fungoides, unspecified site
HCC Category Mapping
V28HCC 20 — Lung and Other Severe Cancers
0.000V24HCC 10 — Lymphoma and Other Cancers
0.675ESRDHCC 10 — Lymphoma and Other Cancers
0.000RxHCCHCC 19 — Lymphoma and Other Cancers
0.000What This Code Means
A rare type of skin cancer (mycosis fungoides) that starts in T-cells and can affect lymph nodes, with the primary site not yet specified.
Coding Tips
- •Mycosis fungoides is a cutaneous T-cell lymphoma; confirm diagnosis through skin biopsy
- •Use this code only when the specific lymph node site is unknown or not documented
Clinical Significance
Mycosis fungoides at an unspecified site is a primary cutaneous T-cell lymphoma that typically presents with progressive skin patches, plaques, and tumors. It is the most common form of cutaneous T-cell lymphoma and follows a typically indolent but chronic course. Accurate coding is important because mycosis fungoides requires different management than other lymphoma types and carries distinct prognostic implications.
Documentation Requirements
- ✓Skin biopsy confirming mycosis fungoides histology with characteristic epidermotropism of atypical T-cells
- ✓Documentation of skin lesion stage (patch, plaque, tumor, or erythrodermic)
- ✓TNMB staging specific to mycosis fungoides if documented
- ✓Documentation of body surface area involved
- ✓Current treatment regimen (topical therapies, phototherapy, systemic agents)
Commonly Confused Codes
C84.10 — Sezary disease, unspecified site: Sezary disease is the leukemic variant of cutaneous T-cell lymphoma with circulating malignant cells; mycosis fungoides is primarily cutaneousC84.40 — Peripheral T-cell lymphoma, unspecified: Mycosis fungoides is a distinct cutaneous T-cell lymphoma with its own clinical behavior and treatment approachL40.0 — Psoriasis vulgaris: Early-stage mycosis fungoides patches can mimic psoriasis; biopsy is essential for differentiation
Code Hierarchy
└C84Mature T/NK-cell lymphomas└C84.0Mycosis fungoides└C84.00Mycosis fungoides, unspecified site
└C84.00Mycosis fungoides, unspecified site