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Basaloid squamous carcinoma (BSC) is an uncommon aggressive variant of squamous cell carcinoma with a predilection for hypopharynx, tongue base, and larynx. We present 5 cases of BSC of unusual sites, each from maxillary sinus, external auditory canal, submandibular gland, tonsil, and nasopharynx. Only a few cases arising in these sites have been reported to date. Patients included 3 men and 2 women with the age range of 45-69 years (mean, 56.4 years). Microscopically, the tumors were characterized by solid lobules and nests of ovoid basaloid cells with abundant desmoplastic stroma. Comedonecrosis, peripheral palisading of tumor cells, trabecular pattern, and rosette-like arrangement were commonly observed. Tumor cells had scanty cytoplasm and their nuclei were ovoid, relatively uniform, and hyperchromatic. In two cases, concomitant squamous cell carcinoma in situ was identified. Immunohistochemical stains revealed that tumor cells were strongly positive for pancytokeratin and negative or weakly positive for p63. Being aware of BSC that can arise from unusual sites would help diagnose correctly and treat properly this rare and distinct clinicopathologic entity.
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