Adamantinoma is a rare form of bone cancer, characterized by its slow-growing nature. It represents less than 1% of all cancers that originate in the bone. This tumor almost exclusively develops in the bones of the lower leg, with most cases occurring in the tibia, or shin bone. Less frequently, it can be found in the fibula (calf bone), and in rare instances, it has been reported in the jawbone, femur, hands, or feet.
The disease most often affects adolescents and young adults between the ages of 20 and 35 and is observed more commonly in males than in females. Due to its slow growth, individuals may have the tumor for a significant period before symptoms become apparent. Although it grows slowly, it is a malignant cancer with the potential to damage surrounding bone and spread to other parts of the body.
Symptoms and Diagnostic Process
The initial signs of an adamantinoma are often subtle due to the tumor’s slow development. Patients experience localized pain in the affected bone, which may gradually worsen over time. A visible or palpable lump on the shin is a common sign, accompanied by swelling and tenderness in the area, which can lead to difficulty with movement or cause a noticeable limp.
Because the tumor weakens the bone’s structural integrity, a fracture resulting from a minor injury can sometimes be the first indication of the underlying disease. The diagnostic process begins with a physical examination and a review of the patient’s medical history.
An X-ray is the first imaging test performed, and it can reveal characteristic features of adamantinoma, often described as having a “soap bubble” appearance. To better understand the tumor’s size, location, and if it has invaded nearby soft tissues, doctors will order more detailed scans such as a Magnetic Resonance Imaging (MRI) or a Computed Tomography (CT) scan.
While imaging provides strong evidence, the definitive diagnosis of adamantinoma is confirmed through a biopsy. During this procedure, a surgeon removes a small sample of the tumor tissue. A pathologist then examines the cells under a microscope to identify the specific characteristics of adamantinoma.
Classifications of Adamantinoma
Following a biopsy, pathologists classify adamantinoma based on its microscopic appearance, which helps in understanding the tumor’s behavior. The “classic” form is defined by a distinct biphasic pattern. It is composed of two types of cells: epithelial cells and a supportive, fibrous tissue known as an osteofibrous component. The proportion and arrangement of these two cell types are important for its identification.
Another classification is “differentiated” adamantinoma, also called osteofibrous dysplasia (OFD)-like adamantinoma. This variant has a predominance of the osteofibrous tissue, with only small, scattered clusters of epithelial cells. This appearance makes it difficult to distinguish from a benign bone condition called osteofibrous dysplasia, which also occurs in the tibia of younger individuals.
The relationship between OFD and adamantinoma is a subject of ongoing scientific discussion. Some researchers theorize that OFD might be a precursor lesion that can develop into a classic adamantinoma over time. Others view them as part of a spectrum, which complicates diagnosis and underscores the need for expert pathological review.
Surgical Treatment and Management
The primary treatment for adamantinoma is surgery. The goal of the operation is the complete removal of the tumor to prevent it from returning. The standard surgical procedure is a wide local excision, which involves removing the cancerous part of the bone along with a surrounding margin of healthy tissue. This clean margin helps ensure that no microscopic cancer cells are left behind, reducing the chance of the tumor recurring.
After a large segment of bone is removed, reconstructive surgery is necessary to restore the limb’s function. The common approach is limb-salvage surgery. In this procedure, the removed section of bone is replaced either with a bone graft (taken from the patient or a donor) or with a custom-made metal prosthesis.
In some situations, if the tumor is very large, has invaded major nerves and blood vessels, or if reconstruction is not feasible, amputation of the affected limb may be necessary. The choice between limb-salvage and amputation is complex and tailored to each individual’s circumstances.
Adamantinomas are highly resistant to both chemotherapy and radiation therapy, so these treatments are not a standard approach for the primary tumor. Chemotherapy may be considered if the cancer has metastasized, but surgery remains the definitive treatment for the original tumor site.
Recurrence and Long-Term Outlook
The long-term outlook for individuals with adamantinoma is positive if the tumor is completely removed. However, the risk of local recurrence, where the tumor returns in the same location, is a concern. Recurrence is often the result of an incomplete initial removal.
There is also a risk of metastasis, where the cancer spreads to distant parts of the body. This can occur in approximately 15-20% of cases, sometimes years after the initial treatment. The most common site for adamantinoma metastasis is the lungs, though it can also spread to lymph nodes or other bones.
Given the risks of local recurrence and late metastasis, lifelong follow-up care is an important part of management. Patients need regular appointments with their oncology team for many years after their surgery. These check-ups include physical exams and routine imaging tests, such as chest X-rays or CT scans, to monitor for any signs that the cancer may have returned or spread.