Case #2 (SqP mimicking SialP at the mouth floor) A 47-year-old Asian male visited the Department of Oral and Maxillofacial Surgery at the Yonsei Dental Hospital complaining of a papillary mass under the tongue that had occurred a month before without a specific event. There was no pain or other remarkable symptoms. He had a past medical history of treated tuberculosis. On clinical examination, an exophytic verrucous mass was observed from the floor of mouth to the lingual frenum (Figure 3A). It had a maximum diameter of about 1.5 cm, and showed a pink surface color similar to the surrounding normal mucosa. In addition, the lesion was soft on palpation, with no observable tenderness or induration. It was excised and submitted for histopathologic examination under a clinical impression of SqP. Low-power histopathological examination revealed an exophytic papillary mucosal epithelium with an underlying adenomatous submucosa compartment (Figure 3B). The submucosa compartment was composed of a "superior" hyperplastic and microcystic-like portion and an "inferior" dilated and tortuous ductal portion (Figure 3C). The superficial papillary mucosa had focal atypical features such as bulbous rete ridges and disorganized basaloid proliferation (Figure 3D). In the superior submucosa portion, the overall epithelial structure was adenomatoid, with hyperplastic squamous epithelium overlined by a layer of ciliated columnar epithelium (Figure 3E). Microcystic or microductal structures were seen within the superior hyperplastic ductal epithelium. In the inferior submucosa portion, indistinct micropapillary-like projections were seen within the dilated columnar ductal epithelium (Figure 3C). The inferior portion lacked any evidence of tumorous adenomatous proliferation. Differential diagnosis between SqP and SialP was required. IHC staining revealed that CK7 was only positive in the ductal epithelium of the inferior portion and in a single layer of luminal epithelium in the superior submucosa portion (Figure 3F). Importantly, diffuse S-100 expression and abluminal SMA staining typically seen in SialP were not seen in this lesion. The superior submucosa portion did not show SMA (+) myoepithelial cells, consistent with a general excretory duct histology rather than the salivary gland tumor, SialP (Figure 3H). These findings indicated a definite tumorous papillary growth in the superficial mucosa with extension to the superior excretory duct and additional presence of reactive ductal dilation.
Although the overall lesion did not present definite cellular pleomorphism or loss of polarity, since the epithelial basal cells showed bulbous architecture, we evaluated the lesion for the possibility of early-stage malignant transformation. The IHC results showed that the Ki-67 proliferation index and p53 expression were minimal and localized at the basal layer in both the lesional epithelium and adjacent normal mucosa (Figure 3I). This pattern suggested that the mild epithelial atypia in Case #2 was more likely to be benign and reactive rather than premalignant, as occasionally seen in SqPs. The final diagnosis was SqP with mild atypia and ductal extension.