## Cutaneous Lymphomas: Classification and Epidemiology **Key Point:** **Mycosis fungoides (MF)** is the most common type of primary cutaneous lymphoma, accounting for approximately 50–60% of all cutaneous lymphomas. It is a **cutaneous T-cell lymphoma (CTCL)** derived from mature CD4+ helper T cells. ### Classification of Cutaneous Lymphomas | Type | Cell Origin | Frequency | Key Features | |------|-------------|-----------|---------------| | **Mycosis fungoides** | CD4+ T cells | 50–60% | Patches → plaques → tumors; indolent course | | **Sézary syndrome** | CD4+ T cells | ~5% | Erythrodermic variant of MF with circulating tumor cells | | **Primary cutaneous DLBCL** | B cells | ~20% | Leg-type (poor prognosis) vs. non-leg-type | | **Cutaneous marginal zone lymphoma** | B cells | ~10% | Indolent; associated with Borrelia in some cases | | **Hodgkin lymphoma (skin)** | Reed-Sternberg cells | <5% | Rare; usually secondary involvement | ### Mycosis Fungoides: Pathological Features **High-Yield:** MF shows a characteristic **epidermotropic lymphocytic infiltrate** with atypical T cells (mycosis cells) that preferentially infiltrate the epidermis, creating a "cerebriform" appearance of nuclei. **Clinical Pearl:** The classic clinical progression is **patch → plaque → tumor** (TNM staging), and early-stage disease (patches and plaques) has an excellent prognosis with median survival >20 years. **Mnemonic:** **CTCL** — **C**utaneous **T**-cell **L**ymphoma; **M**ycosis **F**ungoides is the **M**ost **F**requent type.
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