## **Core Concept**
The question involves identifying an ideal immunohistochemistry panel for a specific type of ovarian tumor, characterized by diffuse sheets of small cells with doubtful nuclear grooving and scanty cytoplasm, in a 30-year-old female. The tumor in question seems to suggest a **small cell carcinoma of the ovary**, possibly of the **hypercalcemic type** given the absence of Call-Exner bodies, which are typically seen in **granulosa cell tumors**.

## **Why the Correct Answer is Right**
The correct answer, **D. Inhibin, Calretinin, WT-1, p53, Ki67**, is appropriate for several reasons:
- **Inhibin** and **Calretinin** are useful in identifying granulosa cell tumors but can also be positive in other tumors.
- **WT-1** is particularly useful in the context of ovarian tumors, as it is often positive in **serous carcinomas** and **small cell carcinomas** of the ovary.
- **p53** is a tumor suppressor protein that, when mutated, can lead to its accumulation in the cell, making it a useful marker for identifying tumors with **TP53** mutations, common in **high-grade serous carcinomas** but also relevant in **small cell carcinomas**.
- **Ki67** is a proliferation marker that helps in assessing the tumor's aggressiveness.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option lacks specificity for the tumor type in question. While **CD45** and **S-100** can be useful in a broad differential, they are not specific enough for the likely diagnosis here.
- **Option B:** **SMA**, **desmin**, and **cytokeratin** might help in identifying mesenchymal or epithelial differentiation but are not the best initial panel for this specific ovarian tumor.
- **Option C:** This panel includes **CEA**, **CA125**, and **vimentin**, which, while useful in some contexts for ovarian tumors, does not specifically target the likely diagnosis here as effectively as Option D.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **small cell carcinoma of the ovary, hypercalcemic type**, often presents in younger women and is associated with **hypercalcemia**. This tumor type does not typically express **inhibin** or **Calretinin** but may show positivity for **p53** and other markers listed in the correct answer.

## **Correct Answer:** D. Inhibin, Calretinin, WT-1, p53, Ki67.