Table 2.

Distinguishing features between CC and its important differential diagnoses

Microscopic features	Carcinoma cuniculatum	Verrucous carcinoma	Conventional Squamous cell carcinoma	Pseudoepitheliomatous hyperplasia
Architecture	Well differentiated squamous lined keratin-filled, burrowing crypts	Mixed exophytic and endophytic growth pattern. Verruciform exophytic component	Solid, irregular nests/islands, squamous pearls may be present	Markedly acanthotic irregular squamous epithelium
Invading front	Deeply located cohesive squamous nests and cryptsa	Broad “pushing” infiltration	Aggressive stromal invasion with desmoplastic response	Tongue-like projections of squamous epithelium. Absence of stromal desmoplasia
Lymphovascular invasion	Not present	Not present	Possible	Not present
Cytologic atypia	Absent to mildb	Absent to mildb	Mild to severe	Absent to mildb
Mitotic activity	Variableb	Variableb	Frequent and atypical	Variable, non atypical

^aMay have superimposed pseudoepitheliomatous hyperplasia, displaying a reticulated network of tongue-like epithelial protrusions resulting in a jagged tumor–stromal interface mimicking aggressive stromal invasion

^bThe degree of cytologic atypia and basally confined mitotic activity may be increased in acutely inflamed areas