Pathology quiz case

A 35-YEAR-OLD MAN presented to a community otolaryngologist with a 1-year history of a painless mass on the dorsum of his tongue. He denied dysphagia, odynophagia, otalgia, fatigue, and weight loss. He had a medical history that was significant only for hypertension that was well controlled with lisinopril. He had a 15-year smoking history of 11⁄2 packs of cigarettes per day but denied any alcohol use. There was no family history of lymphoma or head and neck cancer. On physical examination, there was a 1.1 1.2-cm raised, nontender, firm, erythematous lesion on the dorsum of the tongue in the midline, just anterior to the circumvallate papillae (Figure 1). The lesion was surrounded by an area of leukoplakia. The patient had a normal voice and healthy dentition. His tongue displayed normal mobility. The results of the rest of his head and neck examination were unremarkable. He underwent a biopsy of the lesion in the community otolaryngologist’s office (Figure 2). The pathologic diagnosis was infiltrating moderately differentiated squamous cell carcinoma. The patient was referred to our tertiary care academic medical center for further treatment. The pathology slides were reviewed and a new diagnosis was made. The patient underwent local excision of the lesion, with primary closure of the dorsum of the tongue. The final pathology results confirmed the diagnosis and established that the margins were negative (Figure 3 and Figure 4). The inset in Figure 4 shows immunohistochemical staining for S100 protein (red chromagen). What is your diagnosis?