Mucoepidermoid carcinoma, involving the surface epithelium, not to be confused with OSCC

Introduction

Mucoepidermoid carcinoma (MEC) is the most common primary salivary gland malignancy worldwide. MEC can be categorized histologically into low, intermediate, and high-grade tumor. When the epidermoid component predominates, MEC may mimic oral squamous cell carcinoma (OSCC) which contribute to diagnostic challenge. Meticulous evaluation would be warranted to differentiate between moderate or high-grade MEC and OSCC. Differentiating these two entities is necessary to prognosticate survival and to determine the most appropriate treatment plan.

Case Presentation

A 20-year female presented with painless lesion, persisted for 1-2 years, and hasn’t changed in size for last 6 months. Clinical examination showed 1.5 × 0.5 cm elevated lesion of posterior hard palate with central ulcerated area. Incisional biopsy demonstrated evidence of proliferating tumor islands some of which were connected to overlying surface epithelium. That consisted of predominantly epidermoid cells, with scattered mucinous component. Small cystic islands lined by mucous, intermediate, and epidermoid cells, that contributed to less than 20% of tumor were noted. Mucicarmine and PAS-diastase positive highlighted scattered mucous cells. Tumor cells were p63 positive, and negative for Calponin and GATA-3. Findings were consistent with MEC, low grade. Upon excision, surgical impression included erosion of underlying bone. Excisional biopsy showed tumor infiltration of terminal duct and overlying surface epithelium and more prominent cystic component. S100 highlighted perineural invasion. Final diagnosis of MEC, low grade, according to AFIP classification criteria was rendered.

Conclusion

MEC arising from terminal duct ending in surface epithelium, might be erroneously interpreted as OSCC, especially when predominated with epidermoid cells on small incisional biopsies. Extensive tumor sampling, demonstration of intracellular mucin assisted by special stains, and presence of intermediate cells, represent important clue to diagnosis. It is important to use the most objective histopathologic features to grade MEC and to determine prognosis or treatment modality more accurately.