Infrequent Histopathologic Subtypes of Oral Squamous Cell Carcinoma: A Case Series with Emphasis on Histopathologic Characteristics

Abstract

Squamous cell carcinoma (SCC) is the most common oral malignancy. Conventional types are classified as well-, moderately- and poorly differentiated, which are usually easy to diagnose microscopically. Still, uncommon variants such as basaloid, verrucous, spindle cell, papillary, adenosquamous, acantholytic, cuniculatum, clear cell, and pigmented SCC make a diagnostic challenge for pathologists. This report presents four rare cases of oral SCC with histopathologic diagnosis of spindle cell carcinoma, carcinoma cuniculatum, papillary SCC, and basaloid SCC focusing on microscopic characteristics and differential diagnosis. The apprehensive knowledge about the unique histopathologic features of these uncommon variants is crucial to avoid their misdiagnoses and provide appropriate treatment.

Keywords: Basaloid Squamous Cell Carcinoma; Carcinoma Cuniculatum; Spindle Cell Carcinoma; Squamous Cell Carcinoma.

Figure 1

Spindle cell SCC; a: A large pedunculated polypoid mass of the alveolar ridge of maxilla; b: Spindle cell proliferation and dysplastic superficial epithelium (100×, hematoxylin and eosin staining (H & E)); c: Spindle cell proliferation (100×, H & E); d: Pleomorphic spindle cells with mitosis (400×, H & E)

Figure 2

Spindle cell SCC; a: Positive cytoplasmic immunoreactivity of spindle cells for vimentin and absence of staining of the epithelial island (black arrow) (100×, IHC); b: Positive cytoplasmic immuno-reactivity of epithelial islands for AE1/AE3 (100×, IHC)

Figure 3

Carcinoma cuniculatum; a: “Nest-like” epithelium filled with keratinaceous material (40×, H & E); b-d: Epithelial cells surrounding keratinaceous material show significant mild atypia (100×, H & E)

Figure 4

Papillary SCC; a: Exophytic papillary mass and pigmented areas of the left maxillary alveolar mucosa and palate; b: Multiple papillary projections with fibrovascular cores, in addition to prominent dysplastic changes and severe inflammation can be observed (100×, H & E)

Figure 5

Basaloid SCC; a: A large erythematous proliferative mass with granular surface; b: Basaloid islands with comedonecrosis (black arrow) (100×, H & E); c: Basaloid islands (100×, H & E); d: Keratin pearl formation (black arrow head) (100×, H & E)