**Question:** A Salivary gland tumour, which histologically shows a double layer of epithelial cells based on a reactive lymphoid stroma, is

A. Warthin's tumor
B. Pleomorphic adenoma
C. Lymphoepithelial cyst
D. Mucoepidermoid carcinoma

**Correct Answer:** C. Lymphoepithelial cyst

**Core Concept:**

Salivary gland tumors are a diverse group of lesions that can arise from different cell types within the salivary glands. Histologically, they can be classified based on their cellular composition and stromal characteristics. In this question, we are focusing on tumors with a double layer of epithelial cells surrounded by a reactive lymphoid stroma.

**Why the Correct Answer is Right:**

Lymphoepithelial cyst (LEC) is a benign salivary gland tumor characterized by the presence of a double layer of epithelial cells and a reactive lymphoid stroma. The double layer of epithelial cells consists of both ductal and acinar cells, surrounded by a dense lymphoid stroma. This unique histological feature distinguishes LEC from other tumors with similar epithelial cell layers (e.g., Warthin's tumor, pleomorphic adenoma, and mucoepidermoid carcinoma) that have different stromal components.

**Why Each Wrong Option is Incorrect:**

1. **Warthin's tumor (A):** This is a rare benign salivary gland tumor primarily involving the parotid gland. While it does exhibit a double layer of epithelial cells, it has a lymphoid space separated by a thin fibrous wall, not a dense lymphoid stroma as seen in LEC.
2. **Pleomorphic adenoma (B):** This is a common benign salivary gland tumor with a single layer of epithelial cells surrounded by myoepithelial cells and myxoid stroma. LEC and pleomorphic adenoma differ in the number of epithelial layers and the type of stromal cells.
3. **Mucoepidermoid carcinoma (D):** This is a malignant salivary gland tumor with varying proportions of epithelial components (cuboidal, squamous, and mucus-producing cells), not a double layer of epithelial cells like LEC. Mucoepidermoid carcinoma also has a desmoplastic stroma, not a dense lymphoid stroma as seen in LEC.
4. **Lymphoepithelial cyst (C):** Although this is a benign salivary gland tumor with a double layer of epithelial cells, it lacks a dense lymphoid stroma. Lymphoepithelial cyst is a true cyst containing lymphoid tissue, not a solid tumor with a dense lymphoid stroma like LEC.

**Clinical Pearl:**

Lymphoepithelial cyst (C) is another benign salivary gland tumor with a double layer of epithelial cells but differs from LEC in that it is a true cyst containing lymphoid tissue, not a solid tumor with dense lymphoid stroma. The correct answer is Lymphoepithelial cy