**Question:** Marker of Melanoma is -

A. S100
B. HMB45
C. Melanoma In Situ (MIS)
D. Tyrosinase

**Correct Answer:** .

**Core Concept:**
Melanoma is a malignant tumor derived from melanocytes, the pigment-producing cells in the skin. The identification of specific markers can help in the diagnosis, staging, and prognosis of melanoma.

**Why the Correct Answer is Right:**
Marker of melanoma refers to specific proteins or enzymes that can be identified in melanoma cells, reflecting their origin and characteristics. In this case, the correct answer is B. HMB45 (Heme-45), also known as Microphthalmia Transcription Factor (MITF), is a transcription factor that plays a crucial role in melanocyte development and differentiation. Its expression is specific to melanocytes and melanoma cells, making it a valuable marker in diagnosing and studying melanoma.

**Why Each Wrong Option is Incorrect:**

A. S100 is a marker for Schwann cells, peripheral nerves, and some dendritic cells. Although it can be expressed in melanoma cells, it is not specific to melanoma and can also be found in other cell types.

C. Melanoma In Situ (MIS) is a stage of melanoma, indicating the cancer cells are confined to the epidermis or dermis. MIS is not a marker, but a description of the tumor's location and stage.

D. Tyrosinase is an enzyme involved in the biosynthesis of melanin, the pigment responsible for skin color. Tyrosinase is expressed in melanocytes and can be found in some benign melanocytic lesions, but it is not solely specific to melanoma.

**Clinical Pearl:**
HMB45, along with S100 and MelanA (Melanoma Antigen Recognized by T-cells), are collectively known as "Melanoma Antigen" markers. These markers, along with clinical and histopathological examination, significantly improve the accuracy of melanoma diagnosis and staging, particularly in cases where the tumor is not visually apparent or in cases of atypical pigmented lesions.