Answer: Squamous cell carcinoma, basaloid type

Histology: The tumor is growing as large and expansive lobules within the submucosa. Some of the tumor lobules display prominent comedo-type necrosis. The cells have a high N:C ratio and exhibit pleomorphism, a high mitotic rate, and individual cell necrosis. The individual tumor cells are separated by a pink hyaline matrix. The formation of small ductules is a striking feature. The presence of overt keratinization is a very focal finding. The overlying surface epithelium is relatively unremarkable without significant dysplastic changes.

Discussion: Basaloid squamous cell carcinoma (BSCC) is a histologic variant of squamous cell carcinoma of the head and neck. It is clinically characterized by rapid growth, a propensity for metastatic spread, and a tendency to present at an advanced stage. Although it can arise anywhere in the upper respiratory tract, it has a strong predilection for the pyriform sinus and supraglottic larynx. Squamous cell carcinomas with a prominent basaloid phenotype are also encountered in the oropharynx (base of tongue and palatine tonsils), but these have been found to be a clinically and biologically distinct tumor type that must be differentiated from the highly aggressive basaloid squamous cell carcinoma of the larynx. These basaloid tumors of the oropharynx are usually HPV-positive, and they are associated with much more favorable clinical outcomes. Site alone is generally sufficient to make this distinction. HPV-related basaloid carcinomas tend to be highly restricted to the oropharynx and are not seen with much frequency in the larynx.

Given its prominent basaloid morphology, it can also be easily confused with other basaloid neoplasms including the solid variant of adenoid cystic carcinoma. The presence of matrix deposition and the small ductal structures further enhances the salivary gland-like appearance of this variant and further obscures distinction from the solid adenoid cystic carcinoma. The diagnosis of the basaloid variant squamous cell carcinoma relies heavily on the demonstration of clear-cut squamous differentiation. This may take the form of dysplasia of the overlying surface epithelium, abrupt squamous eddies within the basaloid nests, or a separate component of conventional squamous cell carcinoma. In this particular case, the presence of focal keratinization (together with the absence of clear cut cribriforming structures of classic adenoid cystic carcinoma) confirms the squamous nature and surface origin of this tumor. Sometimes these invasive carcinomas can drop off the basal cell layer in the absence of full thickness dysplastic changes in the surface epithelium. No wonder that the basaloid variant of squamous cell carcinoma may sometimes be mistaken clinically as a salivary gland tumor due to the absence of a visible surface lesion.