A 50-year-old fair skinned male presented to the OPD with elevated plaque and ulcerated hyperpigmented nodule which shows variegation of colour on the back which has been progressively increasing in size. Biopsy of the skin lesion was done. All of the following antibodies can be tested except: –

## **Core Concept**
The clinical presentation described for the 50-year-old fair-skinned male, with an elevated plaque and ulcerated hyperpigmented nodule showing variegation of color on the back that has been progressively increasing in size, is highly suggestive of **melanoma**, a type of skin cancer that originates from melanocytes.

## **Why the Correct Answer is Right**
In the context of melanoma, certain antibodies are relevant for diagnosis and assessing prognosis. **S-100 protein** and **Melan-A (MART1)** are commonly used markers for identifying melanocytic lesions, including melanoma. **Tyrosinase** is another specific marker for melanocytes. However, when considering the options provided (though not explicitly listed), we must focus on the relevance of each antibody to melanoma or skin lesions.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Assuming one of the provided antibodies is specific for a different type of tumor or condition not related to melanoma, it would be incorrect in the context of testing for melanoma.
- **Option B:** If another antibody is commonly used in the diagnostic workup for melanoma or related conditions, choosing this option would not be incorrect.
- **Option C:** Similarly, if an antibody is relevant, it shouldn't be the answer.
- **Option D:** **Ki-67** is a proliferation marker that can be expressed in many types of cells, including melanocytes, but it's not specific for melanoma. However, it's used in a broad sense to assess the proliferative activity of tumors.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that for melanoma, **S-100**, **Melan-A**, and **Tyrosinase** are specific markers. **Ki-67**, while not specific, is useful for assessing tumor aggressiveness. When it comes to specific antibodies for melanoma, focusing on those that are melanocyte-specific is crucial.

## **Correct Answer:** .

✓ Correct Answer: D. Anti-Cytokeratin Ab