Adamantinoma: Symptoms, Diagnosis, and Treatment

Adamantinoma is a rare, low-grade malignant bone tumor that arises almost exclusively in the tibia, the larger bone of the lower leg. It accounts for less than one percent of all primary bone cancers, and it tends to grow slowly compared with other bone malignancies. Because of its rarity and its ability to mimic benign conditions on imaging, adamantinoma often takes years to diagnose. Understanding what to look for, how doctors confirm it, and what treatment involves can make a real difference in outcomes.

Who Gets Adamantinoma and Where It Appears

Most people diagnosed with adamantinoma are between 10 and 30 years old, though cases have been reported in younger children and in middle-aged adults.¹ A study of pediatric cases found the tumor in children as young as three years old, with the tibia involved in every case.² There is no strong sex predilection, though some large datasets suggest a slight male predominance.

The tumor overwhelmingly favors the mid-shaft of the tibia. It can occasionally involve the fibula (the thinner bone running alongside the tibia) as well, and there are scattered reports of adamantinoma appearing in other long bones, but the tibial diaphysis is the classic location.³ This predilection for a single anatomical site is unusual among bone tumors and is one of the features that helps narrow the diagnosis.

Symptoms and How They Develop

The hallmark complaint is a painful, slowly enlarging bump on the front of the shin. Most patients describe a combination of pain and localized swelling that has been present for months or even years before they seek medical attention.¹ The pain tends to be dull, worse with activity, and sometimes dismissed as a sports injury or growing pains in younger patients. In some cases, the tumor weakens the bone enough to cause a pathological fracture, which may be the event that finally prompts imaging.

Because the growth rate is slow and the symptoms can be vague, diagnostic delays of several years are common. A young person with persistent anterior tibial pain and a palpable, firm mass on the shin should have imaging rather than a wait-and-see approach, especially if the symptoms do not respond to rest or anti-inflammatory medication.

What Imaging Reveals

On a standard X-ray, adamantinoma typically appears as an eccentric, lobular, lytic lesion in the tibial cortex with sclerotic borders. Multiple radiolucent areas can overlap, producing what radiologists describe as a “soap-bubble” appearance.⁴ This pattern on a plain film centered in the tibial mid-shaft is highly suggestive, but it is not unique to adamantinoma.

CT scans add detail about how the tumor involves the cortex and are important for checking the lungs for metastases, though CT is limited in showing how far the tumor extends within the bone marrow cavity.⁵ MRI is the most valuable single imaging tool. It shows low signal on T1-weighted sequences and high signal on T2-weighted sequences, helps stage the tumor locally, reveals any soft-tissue extension or skip lesions along the bone, and is critical for planning surgery because it maps out the tumor-free margins surgeons need to preserve.⁵ In short, anyone with a suspicious tibial lesion on X-ray should get an MRI before any treatment decisions are made.

The Diagnostic Challenge With Osteofibrous Dysplasia

One of the trickiest aspects of diagnosing adamantinoma is distinguishing it from osteofibrous dysplasia, a benign fibro-osseous lesion that also appears in the tibial cortex of young patients. The two conditions share overlapping clinical features and imaging appearances, and some researchers have proposed that they sit on a spectrum, with pure osteofibrous dysplasia at the benign end and classic adamantinoma at the malignant end.⁶ In between sits a variant called osteofibrous dysplasia-like adamantinoma, which has the bland appearance of osteofibrous dysplasia but contains scattered nests of epithelial cells that are the hallmark of adamantinoma.

Whether osteofibrous dysplasia can transform into adamantinoma over time remains debated. Some authors have called osteofibrous dysplasia “juvenile adamantinoma,” while others maintain that most cases of osteofibrous dysplasia are entirely unrelated to adamantinoma and never progress.⁷ For the patient, the practical takeaway is that a diagnosis of osteofibrous dysplasia in the tibia warrants careful follow-up, and the tissue sample matters enormously. Pathology, specifically the detection of epithelial cells, is the key tool for separating these overlapping entities.⁸

Biopsy and What the Pathologist Looks For

Adamantinoma is defined by the presence of epithelial cells set within a fibrous or bony stroma. The epithelial component is what distinguishes it from osteofibrous dysplasia and drives its malignant behavior.⁹ Under the microscope, the tumor can take on several patterns. The epithelial cells stain for cytokeratins and for the marker p63, which helps confirm the diagnosis when the epithelial component is subtle.¹⁰

A needle biopsy can sometimes miss the epithelial nests, especially in osteofibrous dysplasia-like variants where these cells are sparse. In one series, three out of 19 cases were initially classified as osteofibrous dysplasia on needle biopsy but upgraded to classic adamantinoma when the full surgical specimen was examined.¹¹ Radiological features helped flag those cases as potentially more aggressive than the biopsy suggested. This underscores why imaging and pathology need to be interpreted together, ideally by a multidisciplinary team experienced with bone tumors. A biopsy result that says “osteofibrous dysplasia” but imaging that looks more aggressive should prompt additional sampling or heightened surveillance.

Surgical Treatment

Surgery is the definitive treatment for adamantinoma. Conventional chemotherapy and radiation therapy play no meaningful role in managing this tumor.¹² The standard operation is wide excision, meaning the surgeon removes the tumor along with a margin of healthy bone and soft tissue on all sides. Limb-salvage surgery is the goal in the vast majority of cases. In a multicenter review, roughly nine out of ten patients underwent a limb-salvage procedure rather than amputation.¹²

The single most important factor for preventing recurrence is achieving clean, or “uncontaminated,” resection margins. A large international study of 318 cases found that clean margins dramatically reduced the risk of local recurrence. The same study identified pathological fracture as a risk factor for recurrence, and noted that female sex was associated with a somewhat lower recurrence risk compared to males.¹³ Curettage alone, where the tumor is scraped out rather than excised with surrounding tissue, carries a much higher recurrence rate. In one smaller series, every patient treated with curettage experienced a local recurrence, compared with about three in ten after en bloc resection.¹⁴ This is why current practice strongly favors wide resection rather than conservative scooping.

Rebuilding the Bone After Resection

Removing a segment of the tibia leaves a gap that needs to be bridged for the patient to walk again. Several reconstruction options exist, and the choice depends on the size of the defect, the patient’s age, and the surgeon’s experience.

Vascularized fibula graft: The surgeon transfers a segment of the patient’s own fibula, along with its blood supply, into the tibial defect. Because the graft stays alive, it heals by direct bony union rather than the slower creeping-substitution process. Over roughly 18 months, the transplanted fibula hypertrophies to bear the loads normally handled by the tibia.¹² In a pediatric and adolescent series, all ten patients achieved bone union at a mean of about 12 months, and graft remodeling reached roughly 94 percent at two years. The average functional score at long-term follow-up was high, though complications like graft fractures and infection did occur.¹⁵
Allograft: A donor bone segment is used to fill the gap. About half the patients in one large multicenter review received an intercalary allograft. Allograft heals more slowly through creeping substitution, and it carries risks of delayed union, non-union, infection, and fracture.¹²
Endoprosthesis: A custom metal implant replaces the missing bone segment. This enables an earlier return to function and avoids donor-site complications entirely, though revision rates and mechanical complications over many decades of use are concerns, particularly in young patients. One series of custom tibial diaphyseal replacements reported a mean functional score of 23 out of 30 and noted that while complication and revision rates were high, the approach did not compromise survival.¹⁶

For younger patients who still have years of growth ahead, the choice of reconstruction is especially consequential. A biological graft like a vascularized fibula can grow and remodel, whereas a metal implant may need lengthening or replacement as the child matures. Discussions about reconstruction should happen at a specialized bone-tumor center where surgeons handle these cases regularly.

Long-Term Prognosis

Despite being malignant, adamantinoma carries a substantially better prognosis than most bone cancers. An analysis of 92 patients drawn from the U.S. Surveillance, Epidemiology, and End Results database found a five-year survival rate of about 99 percent and a ten-year survival rate of about 92 percent.¹⁷ A Japanese registry study similarly found that the vast majority of patients had no evidence of disease at follow-up.¹⁸

That said, the tumor can recur locally and, in a minority of cases, spread to the lungs. Recurrences can appear many years after the initial surgery, which is why long-term follow-up with periodic imaging is standard. Patients who undergo adequate wide resection with clean margins have the lowest recurrence risk. When recurrence does develop, it is usually in the local surgical site and can often be managed with repeat surgery. Pulmonary metastases are less common but represent a more serious development, requiring resection of the lung nodules when feasible.

Molecular Research and Emerging Targeted Therapy

Because adamantinoma is so rare, molecular characterization has lagged behind that of more common cancers. Recent work is beginning to fill in the blanks. Whole-exome sequencing of adamantinoma samples found that the gene KMT2D, which is involved in chromatin remodeling, was altered in roughly four out of ten tumors tested. A novel gene fusion, EPHB4-MARCH10, was also identified in one case.¹⁹ Separately, classic adamantinoma samples have shown multiple copy number gains involving chromosomes 7, 8, 10, 12, and 19, along with individual cases harboring an NRAS mutation or a rearrangement involving FGFR1.²⁰

None of these findings have yet translated into routine clinical testing or approved targeted drugs. However, a single case report offers an intriguing glimpse of what molecularly guided therapy might achieve. A young woman with metastatic adamantinoma whose tumor harbored an XRCC2 frameshift mutation received the PARP inhibitor olaparib as a fourth-line treatment and had a sustained clinical response lasting 15 months. When the disease progressed, she was switched to a combination of atezolizumab and bevacizumab, which kept the tumor stable for another eight months. Her overall survival on molecularly guided treatment reached 25 months.²¹ One patient is not a trend, but it illustrates the potential for genomic profiling to uncover actionable targets in a cancer that has historically had no drug options at all.

Adamantinoma-Like Ewing Sarcoma Is a Different Disease

A condition called “adamantinoma-like Ewing sarcoma” occasionally causes confusion because of the shared name. Despite some overlapping features on immunohistochemistry, including expression of keratins and p63, this tumor is genetically distinct from true adamantinoma of long bones. Adamantinoma-like Ewing sarcoma harbors the EWSR1 or FUS fusions characteristic of the Ewing sarcoma family and segregates into its own methylation cluster, separate from conventional Ewing sarcoma.²² It behaves more aggressively than classic adamantinoma, with recurrence and metastatic disease reported in a substantial proportion of cases. The name similarity is purely historical, and the two tumors require different treatment approaches. If you encounter the term “adamantinoma-like Ewing sarcoma” in a pathology report, it refers to a variant of Ewing sarcoma, not to the tibial adamantinoma discussed throughout this article.