Can Ameloblastomas Turn Malignant or Cancerous?
Ameloblastoma is an aggressive odontogenic jaw tumor, accounting for nearly 14 percent of all jaw-based tumors and cysts. In fact, it is considered one of the most prevalent odontogenic tumors in developing countries worldwide. From a histological perspective, ameloblastoma tumors closely resemble the structures of the enamel organ of a developing tooth bud. Despite this similarity, this highly aggressive and distinct tumor demonstrates clinical invasiveness and indeed exhibits an aggressive growth pattern.
Ameloblastoma is primarily classified as a benign tumor that originates within the odontogenic epithelium. It is composed of a mature yet fibrous stroma lacking ectomesenchymal content. Despite its benign nature and epithelial origin, this tumor can have severe clinical implications due to its locally aggressive growth pattern. Particularly when left untreated, nearly 70 percent of cases may exhibit a tendency for malignant or cancerous transformation. In severe cases, up to two percent of malignant ameloblastomas can metastasize to distant sites or involve organ systems.
What Is the Classification of Ameloblastoma by WHO?
According to the report established by the World Health Organization (WHO), which classifies all odontogenic tumors, ameloblastoma is currently categorized into two divisions: benign or malignant types of tumors. Its variability or pattern depends mainly on its biological behavior. Based on this classification report, each type of ameloblastoma has been further subdivided into four subtypes. The WHO classification takes into consideration the factors of the anatomic location of the tumor and its histopathology. In terms of frequency, the benign ameloblastomas are the main variants of this tumor. These are classified into the following four types:
- Solid or multicystic variant of ameloblastoma.
- Unicystic variant of ameloblastoma.
- Peripheral or the extraosseous variant of ameloblastoma.
- Desmoplastic variant of ameloblastoma.
Only two percent of benign tumors have the potential for malignant transformation, making malignant ameloblastomas or tumors relatively rare in dental research or literature. However, they are further classified into:
- Metastasizing ameloblastoma.
- Primary ameloblastic carcinoma.
- Secondary intraosseous ameloblastic carcinoma.
- Secondary peripheral ameloblastic carcinoma.
What Are the Main Variants of Ameloblastoma Tumors?
The main variants of ameloblastoma tumors are classified based on their anatomic location within the jaw and histological observations. These variants help provide the most appropriate diagnosis for dental or maxillofacial surgeons.
1. Multicystic or Solid Ameloblastoma: This variant is considered the most common type of ameloblastoma and is also known as the conventional type tumor because it accounts for nearly 91 percent of all cases of ameloblastoma. These benign jaw tumors grow slowly, and histologically, the solid variant displays two distinct patterns that confirm their diagnosis. These tumors exhibit either a follicular pattern or a plexiform-type pattern. Upon histologic observation, the follicular type shows the proliferation of odontogenic epithelial cells arranged as islands, whereas the plexiform type shows an arrangement of epithelial cells continuously as anastomosing strands. In some multicystic tumors, it is not uncommon to observe both types, that is, both follicular and plexiform patterns. Several histological subtypes exist for this major variant, such as cystic, granular, spindle cell, acanthomatous, basal cell, clear cell, and more. Regardless of the subtype, these histologic patterns are classified under the multicystic or solid variant of ameloblastoma.
2. Unicystic Ameloblastoma: The unicystic ameloblastoma is considered the second most common type, accounting for 5 to 15 percent of all ameloblastoma cases. This variant exhibits a specific predisposition in younger age groups, typically between the second and third decades of life, with documented cases showing an average age of 25 to 26 years. The unicystic variant is an asymptomatic benign tumor presenting as a swelling, primarily located in the posterior mandible region. Interestingly, most unicystic variant ameloblastoma tumors resemble the structure of a dentigerous cyst of an unerupted tooth. Therefore, it is crucial for the oral surgeon to establish a differential diagnosis and confirm post-histopathologically.
Similar to the multicystic variant, which has two types of patterns, the unicystic variant also has two main histopathological variants: the luminal and mural types. In the luminal variant of unicystic ameloblastomas, the cystic pattern of cells is lined by epithelium protruding into the lumen. In contrast, the mural variant displays a follicular or plexiform arrangement of multiple epithelial cells within the cyst's wall. In this unicystic variant too, It is not uncommon to see both luminal and mural types of cell arrangement histopathologically.
3. Peripheral Ameloblastoma: This variant of ameloblastoma may be the least common, with only 1 percent of ameloblastoma tumors falling within this category. Middle-aged patients are most affected, with the average age being 50 to 52 years. The lesions of the peripheral variant are more commonly observed in the mandible (lower jaw) than in the maxilla (upper jaw). Occasionally, they can even be present on the posterior gingiva or gums or in the alveolar sulcus. Histologically, the peripheral ameloblastoma variant comprises islands of epithelium with an extremely similar histological pattern to that of the solid or multicystic ameloblastoma variant. Hence, the location of the tumor can help differentiate this variant from the multicystic variant.
4. Desmoplastic Ameloblastoma: Desmoplastic ameloblastoma is an uncommon but slow-growing, painless variant of ameloblastoma tumors with specific radiological features displaying mixed radiolucent or radiopaque pattern lesions with irregular borders. The histological feature of this variant includes extensive stromal cell islands comprising odontogenic epithelium of variable shapes and sizes. These proliferating islands are enclosed in collagenous connective tissues with collagen fibers causing compression of the cells within. Overall, the histological pattern of this variant gives a bizarre shape or size to the cell islands, confirming the desmoplastic variant. A unique and potentially complicating feature of the desmoplastic variant of ameloblastoma is that it may comprise metaplastic or cancerous bone formation often.
What Is the Management of Ameloblastoma Tumors?
Based on these variants, their aggressiveness or spread, and location, conservative surgical treatment is the mainline treatment for ameloblastoma tumors. These tumors are mainly treated by conservative surgical excision with the oral surgeon aiming to preserve the form and function of the jaw. Enucleation, marsupialization, cryotherapy, and curettage are the main line strategies adopted by the maxillofacial surgeon.
Conclusion
Ameloblastomas are common odontogenic benign jaw tumors with a scope for malignant transformation when left untreated. Hence, it is important for timely diagnosis and management by the oral surgeon to ensure the quality of life, jaw form, and functions in affected individuals. Knowing the different variants based on the histology and location can give the oral surgeon the confirmative diagnosis from other common oral cysts or lesions, and help to determine the correct treatment strategy to be adopted based on the variant and extent of ameloblastoma tumors.
