Ameloblastic carcinoma is a rare malignant odontogenic tumor. Here we present a case of malignant transformation of ameloblastoma into ameloblastic carcinoma over a period of eight years. A cystic lesion in the left mandible was initially identified histopathologically as ameloblastoma, and curettage of the lesion was performed. Recurrence occurred 7 years later, and was treated with a second enucleation and curettage of the tumor. The second histopathological diagnosis was also ameloblastoma. One year later the patient presented with a swelling on the left side of the retromolar triangle. An incisional biopsy detected cytological atypia, and the histopathological features met the criteria for diagnosis of ameloblastic carcinoma. Surgical treatment with segmental mandibulectomy and reconstruction with a free vascularized fibula bone graft was performed. A literature review was performed identifying a total of 234 cases of ameloblastic carcinoma reported. The median age of onset was 47 years, with a peak incidence during the third- and sixth decades. A predominance of men was found, with a male-female ratio of 2,21:1. The tumor was more frequently reported in the mandible, with a mandible-to- maxilla ratio of 1,96:1, and the most common tumor site was the posterior mandible. Surgical treatment was the primary treatment modality and was performed in 87,2% of the patients. Recurrence was reported in 22,2% of the patients, and metastasis in 18,8%. The most common sites for metastasis were the lungs, followed by regional lymph nodes and the brain.
Malignant transformation of ameloblastoma is rarely encountered.
Segmental resection with wide margins is the preferred treatment.
Benign and malignant histological features can be present in the same tumor.
Adequate initial surgical treatment may prevent development of malignant neoplasms.
Ameloblastic carcinoma (AC) is a rare malignant neoplasm arising from odontogenic epithelium. AC may arise de novo , from transformation of a long-standing primary benign lesion, or from benign lesions that have undergone several surgical excisions. The clinical features and histopathological characteristics of AC are comparable to those of ameloblastoma [ ]. Radiologically, a radiolucent uni- or multilocular lesion with destruction of alveolar bone is typically found, and in some cases focal radiopacity may also be detected [ ]. AC combines the histopathological features of ameloblastoma with focal areas of cytological atypia [ ]. This report presents a case of AC, which arose from a previously diagnosed ameloblastoma that underwent malignant transformation over a period of 8 years. Clinical and histopathological features are described, and treatment modalities are discussed. Also, a literature review was performed, comprising the reported data of AC in the English language literature.
Presentation of case
A healthy 36- year old female was referred in May 2019 for assessment of a swelling on the left side of the mandible. Her chief complaint was tenderness in the area and total anesthesia of the inferior alveolar nerve (IAN) after previous surgery. A minor facial asymmetry was found in the mandibular angle. The oral mucosa was intact, but a poorly demarcated swelling was observed. It was mildly tender, hard in consistency and with diffuse margins. She had been treated abroad in 2011 with enucleation of a cystic lesion histologically diagnosed as a follicular type ameloblastoma ( Fig. 1 ). A recurrence had occurred in 2018, and a second enucleation performed. A panoramic radiograph showed a radiolucent lesion on the left posterior alveolar ridge of the mandible ( Fig. 2 ). A 3 x 2,5 cm tumor with resorption and expansion of the lingual cortex extending into the soft tissue was found on CT and MRI. Cervical lymph nodes showed no enlargement or change in size, and no metastatic lesions were found in the lungs or mediastinum. Based on the clinical and radiological findings, a recurrent ameloblastoma was suspected, and an incisional biopsy was performed under local anesthesia. The histopathological examination showed a tumor with poorly defined periphery with sheets and variably sized islands of ameloblastoma-like appearance. Some of the smaller islands had architectural features of benign ameloblastoma. However, the basal nuclei showed a speckled chromatin pattern even in the most highly differentiated areas. The islands retained ameloblastoma-type architecture, but there was a marked expansion of the basal compartment, loss of typical stellate reticulum features and central keratinization. A few islands showed loss of organization with basaloid cells seen centrally. The basal cells had large and very crowded nuclei with speckled chromatin and up to 3 small nucleoli. Mitoses were fairly frequent and occasionally abnormal, and some were found in the stellate reticulum areas. The larger sheets showed central necrosis with peripheral apoptotic degeneration ( Fig. 1 ). The margins were poorly defined with islands showing genuine invasion between the pre-existing collagen bundles and not limited by the periosteum. The proliferation marker Ki-67 showed higher proliferation index than normally seen in benign ameloblastomas, mainly limited to the basal compartment ( Fig. 1 ). A BRAF V600E mutation was detected identical to those seen in benign ameloblastomas. Based on the histopathological findings, the diagnosis of AC was made. Established protocol for surgical treatment of carcinoma of the mandible with segmental resection including the mandibular canal was followed. A segmental mandibulectomy and supraomohyoid lymph node dissection were performed. The tumor was removed with approximately 1 cm margin and the mandible was reconstructed with a free vascularized fibula flap ( Fig. 3 ). The histopathological features of the resected tumor were similar to the incisional biopsy and resection margins were free of tumor cells. Chemotherapy or radiation therapy was not performed. The patient made an uneventful recovery. There were no signs of recurrence 6 months after surgery, and the patient is satisfied with the functional and esthetic outcome ( Fig. 4 ).