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* From the Mount Sinai Hospital (Dr. L. Ciment), Miami Beach, FL; and Robert Wood Johnson Medical Center (Dr. A. Ciment) New Brunswick, NJ.
Correspondence to: Lawrence M. Ciment, MD, FCCP, 3420 Chase Ave, Miami Beach, FL 33140;
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Abstract |
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Key Words: ameloblastoma • electron beam CT • malignant • metastatic • metastatic ameloblastoma • positron emission tomography scan • recurrent ameloblastoma
We describe a case of a 55-year-old man presenting with a metastatic malignant ameloblastoma 29 years after the primary tumor was resected. This represents the longest period between initial diagnosis and first subsequent metastasis recorded as a case report. This case illustrates distinctions between the terms metastatic and malignant; it also highlights the difficulties derived from the accumulation of data by new diagnostic modalities (electron beam CT [EBCT] and positron emission tomography [PET]) and their integration into assessment algorithms.
Ameloblastomas represent 1% of all jaw tumors. They generally are regarded as benign tumors; however, since over half of resected tumors recur, several authorities consider ameloblastomas locally malignant but not metastasizing.1 Metastases, however, are known to occur in roughly 2 to 5% of cases. Over 80% of such metastases involve the lung.2 3
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Workup included CT scan of the abdomen, bronchoscopy, and blood tests, the findings of which all were normal. An F-18 fluorodeoxyglucose-PET scan failed to reveal any increased metabolic activity at any of the corresponding anatomical lesions identified on EBCT. Mandibular and maxillary radiographs showed no local recurrence. A diagnostic thoracotomy revealed metastatic malignant ameloblastoma (Fig 1 ). No treatment was offered, and the patient remained in stable condition for an additional 18 months.
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Discussion |
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Fewer than 45 cases of ameloblastoma with metastases have been reported. Though it is locally aggressive with a high recurrence rate (50 to 72%), the fact that ameloblastoma rarely metastasizes explains why it is considered benign.4 The lung is the most frequent site of metastases, occurring in up to 88% of disseminated cases. The next most frequent metastatic sites were regional lymph nodes, pleura, vertebra, skull, diaphragm, liver, and parotid gland.5
Many factors have been associated with the likelihood of developing metastases. Metastatic tumors occur usually in cases of long duration with multiple surgical procedures or radiation therapy. Extensive local disease and mandibular focus of the primary tumor also tend to be associated with development of metastases.6
Although tumor cells have been found invading blood vessels supporting the concept of hematogenous spread, Vorzimer and Perla7 have suggested that aspirated neoplastic cells were often the cause of pulmonary metastases. Finally, the incidence of lymph node metastatic disease argues for lymphatic dissemination as well.6 8
In 1989, Laughlin8 reviewed 43 patients with previously documented cases of metastatic ameloblastoma; the disease-free interval between diagnosis of tumor and appearance of metastases was 9 years, and the median survival time after metastases was 2 years. In 1993, Sheppard et al9 reviewed cases metastatic to the lungs and found that time from initial diagnosis to pulmonary metastases ranged from 0.3 to 31 years, with a mean of 12.1 years. The time from appearance of metastatic disease until death ranged from 3 months to 5 years, with a mean of 16 months for the 24 patients with sufficient follow-up. In the vast majority of cases, there was a recurrence of the primary tumor before the appearance of spread to the lungs.
Metastatic ameloblastoma can be diagnosed accurately by transbronchial biopsy. Whereas imaging that displays multiple nodules to the lung concurrent with a history of multiple recurrences of the primary ameloblastoma may be suggestive of a metastatic lesion, only a biopsy is truly diagnostic. A thoracotomy has developed into the diagnostic test of choice since it can be simultaneously therapeutic. The utility of the PET scan may lie in its negativity coincident with pulmonary nodules of clinically significant size. This would suggest a more indolent process with a low mitotic rate and would thereby influence the differential diagnosis.
The treatment for metastatic ameloblastoma has been somewhat elusive. In 1987, Lanham5 reviewed chemotherapeutic options and noted that doxorubicin, 5-fluorouracil, 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea, methotrexate, methotrexate with cyclophosphamide, cyclophosphamide, nitrogen mustard, vincristine, prednisone, bleomycin, 5- fluorouracil with dacarbazine, and 5-fluorouracil with doxorubicin did not produce any effective objective improvement. Whereas various studies10 11 have shown that ameloblastoma has responded unpredictably to radiation, Elliason et al11 point out that early radiotherapy failures occurred before development of megavoltage external irradiation. Significant resection with preservation of as much viable lung tissue as possible has been the treatment of choice, as this is the only way to offer a significant disease-free survival. In their 1993 case report, Sheppard et al9 reported a patient who underwent eight thoracotomies before achieving disease-free status with no limitation of activities.
Our case is unique for a number of reasons. The time interval between the diagnosis of primary tumor and subsequent evidence of metastatic pulmonary disease was 29 years, 16 to 19 years more than the mean of previously reported metastatic ameloblastoma cases. It is important to note that the metastatic lesions in our case were discovered only incidentally, the patient discovering them after undergoing a screening EBCT to assess his cardiac function. As EBCT is being used more often to evaluate cardiac function and disease, the conundrum of lung cancer screening is resurfacing.12 EBCT scans performed as screening procedures have the ability to provide high-resolution images and often present us with diagnostic dilemmas: to what extent is it cost-effective to pursue pulmonary irregularities incidentally discovered on cardiac screening? The findings of two previous Japanese nonrandomized studies13 14 on prevalence screening using low-dose CT with sputum sampling did not demonstrate clear decreases in mortality. A 1999 Mayo Clinic trial and the American College of Radiology Imaging Network have ongoing investigations, but no definitive evidence exists as to whether radiography for screening purposes has any impact on mortality.15 Our case highlights the efforts necessary to pursue the diagnosis entailed by the discoveries made available by these newer modalities; cost effectiveness remains to be elucidated.
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Received for publication May 1, 2001. Accepted for publication September 11, 2001.
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