**2. Epithelial tumors**

Squamous cell carcinoma (SCC) and malignant melanoma are common epithelial lesions that require IHC.

#### **2.1. Squamous cell carcinoma**

#### *2.1.1. Definition*

SCC is a malignant neoplasm arising from the squamous epithelium of the oral cavity most commonly from the lip, then tongue, floor of mouth, gingiva, palate, and buccal mucosa. Premalignant changes present as white (leukoplakia) or red (erythroplakia) mucosal patches.

#### *2.1.2. Immunohistochemical stains*

Squamous carcinomas are nearly always positive for CK.

**•** Common CK expression in squamous carcinomas includes AE1/AE3 and CKs 5, 5/6, 14, and 17.


**Figure 1.** a) Squamous cell carcinoma (H&E). b) Cytokeratin stains in SCC.

#### **2.2. Mucosal melanoma**

#### *2.2.1. Definition*

Malignant mucosal melanoma (MMM) is a neural crest–derived neoplasm originating from melanocytes and demonstrating melanocytic differentiation.

#### *2.2.2. Immunohistochemical stains*

S100 protein, Melan A, HMB45, tyrosinase, vimentin are positive, Keratin and muscle markers are negative (Figure 2). [6-13]

**Figure 2.** a) Mucosal melanoma (H&E) b) IHC staining for HMB-45
