Intraosseous mandibular clear cell odontogenic carcinoma with predominant small round blue cells: a potential diagnostic pitfall.

Objective: Clear cell odontogenic carcinoma (CCOC) is a rare malignancy of the jaw, presenting significant diagnostic challenges. This report aims to highlight the complexities associated with biopsy-based diagnoses of oral and maxillofacial lesions, as demonstrated in a case of intraosseous mandibular CCOC initially suggestive of Ewing's sarcoma due to its presentation with small round blue cells.

Results: The patient, a 37-year-old male, presented with a mandibular lesion that on incisional biopsy was suggestive of Ewing's sarcoma. Subsequent, comprehensive histologic evaluation after definitive resection via mandibulectomy revealed a CCOC, characterized by a biphasic pattern of clear and basaloid cells. Histological examination confirmed the presence of glycogen-rich clear cells, supported by periodic acid-Schiff (PAS) staining and confirmed by PAS diastase staining, which demonstrated glycogen digestion. Immunohistochemistry was positive for AE1/AE3, p40, and p63, while negative for c-kit and CD34, confirming CCOC and excluding other malignancies such as Ewing's sarcoma, which would have been treated with neoadjuvant chemotherapy instead of primary surgical treatment as in CCOC.

Conclusion: This case highlights the essential need for thorough histopathological evaluation and the value of a second opinion via additional histologic consultation, particularly due to the diagnostic challenges of heterogeneous lesions in the oral and maxillofacial region.