**Question:** Mycosis fungoides mainly affects

A. Skin and mucous membranes
B. Lymph nodes
C. Blood vessels
D. Hair follicles

**Core Concept:** Mycosis Fungoides is a type of non-Hodgkin lymphoma, which is a group of cancers originating from lymphocytes. In this case, lymphocytes are T cells, a type of white blood cell involved in immune response. Mycosis Fungoides primarily involves the skin, as it starts as a skin cancer (cutaneous T-cell lymphoma) and later may spread to lymph nodes, blood, and other organs.

**Why the Correct Answer is Right:** The correct answer (A) reflects the initial presentation of Mycosis Fungoides, as it starts as a skin cancer affecting the upper layers of the skin (epidermis and dermis). This skin involvement presents as patches, plaques, nodules, or tumors, and may be scaly, red, or pigmented, and can affect various skin areas.

**Why Each Wrong Option is Incorrect:**

B. Lymph nodes are not the primary site of onset for Mycosis Fungoides. Although it can spread to lymph nodes later during its progression, the correct answer (A) focuses on the initial presentation.

C. Blood vessels are not the primary site of Mycosis Fungoides. Its origin is the skin, not blood vessels.

D. Hair follicles are not the primary site of Mycosis Fungoides. The disease affects the skin, not hair follicles.

**Clinical Pearl:** Mycosis Fungoides is the most common type of cutaneous T-cell lymphoma, accounting for approximately 50% of all primary cutaneous lymphomas. It is essential to understand the correct presentation of the disease for accurate diagnosis and appropriate management.