Primary Intraosseous Adenoid Cystic Carcinoma with Widespread Skeletal Metastases Showing Features of High-Grade Transformation

Malignant salivary gland carcinomas arising primarily within the jaw bones are extremely rare. The most common salivary malignancy in these locations is mucoepidermoid carcinoma followed by adenoid cystic carcinoma and adenocarcinoma. The clinical picture and imaging studies of these malignancies may be confused with odontogenic lesions which are more common in this location. Adenoid cystic carcinomas have a prolonged clinical course, tendency for perineural invasion and distant metastasis and multiple recurrences. The diagnosis of these tumors requires thorough histopathologic examination. Immunohistochemical studies may be required in cases showing solid growth pattern. High-grade transformation, earlier termed as dedifferentiation, has been observed in several salivary gland carcinomas including adenoid cystic carcinoma. These transformed tumors are reported to have an extremely poor prognosis. Here, we report a case of primary intraosseous adenoid cystic carcinoma with extensive skeletal metastases which showed a negative staining with p63 and positive staining with CD117. The tumor had a predominant solid growth pattern with areas indicative of high-grade transformation. A negative p63 staining may indicate an incomplete or focal loss of abluminal layer and this is one of the criteria for high-grade transformation in adenoid cystic carcinoma.