Osteopontin: Marker for Mesothelioma
According to a recent article published in the New England Journal of Medicine, the protein osteopontin, which can be found in circulating blood, may help in the early detection of mesothelioma. However, further studies are necessary to confirm osteopontin as a reliable marker as well as to determine if outcomes for patients can be improved through the use of this marker.
Malignant pleural mesothelioma is a rare cancer that develops in the tissue that covers the lungs and lines the interior of the chest. The majority of individuals who develop malignant pleural mesothelioma have a history of chronic exposure to asbestos.
The only curative treatment for mesothelioma is surgery. However, more than 70% of patients diagnosed with mesothelioma have advanced disease, which places them beyond the benefits of surgery. Therefore, the development of a blood test that would allow early diagnosis in patients at risk of mesothelioma-or that would accurately predict a response to treatment-would be a great advance in the management of this malignancy.
Osteopontin is a type of protein that is involved in communication between cells, including signaling involved in the development of cancer. Osteopontin has also been linked to processes involved in cancer progression and spread. Furthermore, it can be found in circulating blood and would therefore be easily measured in individuals at a high risk of developing specific types of cancer.
In order to evaluate osteopontin as a potential marker for mesothelioma, researchers from several institutions conducted a clinical study to compare osteopontin levels in patients diagnosed with mesothelioma and patients with benign (non-cancerous) lung conditions. This study included 76 patients who had been diagnosed with mesothelioma, 69 individuals who had asbestos-related benign lung conditions and 45 healthy individuals who had not been exposed to asbestos. All individuals had their blood drawn and tested for osteopontin levels.
Overall, osteopontin levels were strongly associated with mesothelioma:
• Osteopontin levels were significantly higher in the group of patients diagnosed with mesothelioma compared to those individuals with asbestos-related lung complications (133 ng/ml versus 30 ng/ml, respectively).
• Osteopontin levels were not significantly different between individuals with asbestos-related lung conditions and those who were never exposed to asbestos.
• Osteopontin levels correctly identified nearly 78% of patients with mesothelioma, and accurately distinguished between mesothelioma and benign lung conditions at a rate of 85.5%.
• Osteopontin could accurately identify individuals with stage I mesothelioma (earliest stage – prior to spread), as well as those with advanced disease.
The researchers concluded that osteopontin may be a promising marker for the detection of mesothelioma. Furthermore, osteopontin identified patients with early-stage mesothelioma, a stage at which surgical removal is possible. However, further studies are necessary to confirm these findings, as well as determine whether early detection through osteopontin can improve survival.
Patients who have been exposed to asbestos may wish to speak with their physician regarding the risks and benefits of osteopontin testing or the participation in a clinical trial further evaluating screening measures for this disease. Two sources of information regarding clinical trials include the National Cancer Institute (cancer.gov) and www.cancerconsultants.com.
Reference: Pass HI, Lott D, Lonardo F, et al. Asbestos exposure, pleural mesothelioma, and serum osteopontin levels. New England Journal of Medicine. 2005;353:1564-1573.
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