Primary intraosseous adenoid cystic carcinoma of the mandible: a comprehensive review and analysis of four new cases with emphasis on morphologic, immunophenotypic, and molecular characteristics.

OBJECTIVE: To comprehensively review the clinical manifestations, imaging, diagnosis, treatment, and pathologic features of primary intraosseous adenoid cystic carcinoma (PIACC) of the mandible and analyze PIACC histopathology and molecular features in four cases. STUDY DESIGN: We reviewed the literature and retrospectively studied four cases of PIACC. RESULTS: The clinical and imaging findings of PIACC are similar to other malignant or borderline-malignant mandible tumors. The four cases of PIACC included three males and one female (aged between 41 and 58 years). The histopathologic features of the tumors resembled those of ACC. We observed abundant osteoclasts resorbing bone at the leading edge of the tumors characterized by solid structure histology but not by the cribriform subtype. Additionally, all four cases showed abnormalities in the MYB gene and high expression of MYB protein. All patients survived for the duration of follow-up, and two patients had distant metastases (followed up for 3 to 36 months). CONCLUSIONS: PIACC is extremely rare and is often clinically misdiagnosed. Different histologic subtypes could show different mechanisms of invasion of the mandible. MYB gene and protein expression abnormalities can be used as indicators for the precise diagnosis of PIACC.