Blood tests for cancer(s) have been widely sought after. It could be so easy. Order a test, voila a diagnosis. So far, only one blood test is widely use to screen for cancer, the PSA and it is not without detractors and critics and the issue of screening is contentious.Generally blood tests for cancer have looked pretty good early on only to disappoint as more data is accumulated. But hope springs eternal.
There is recent data that at least suggests a blood test may be useful in the diagnosis of mesothelioma. Ostopontin, a glycoproten that mediates cell matrix interactions and is overexpressed in mesothelioma, may be of value to distinguish patients with asbestos exposure who do and who do not have mesothelioma. The October 13, issue of NEJM features an article by H. I .Pass et al who studied 76 patients with pleural mesothelioma as well as 69 patients with nonmalignant asbestos disease and 45 subjects with no history of asbestos exposure.Tumor tissue was examined for osteopontin and serum levels were measured. Levels were not increased from asbestos exposure alone and patients with pleural plaques and no pulmonary fibrosis did not demonstrate an increased blood level but mesothelioma patients did. 36/38 cases of mesothelioma studied demonstrated osteopontin staining of tumor cells.
Osteopontin, however, cannot be cannot be called MSA ( mesothelioma specific antibody) because colon cancer cases have also shown overexpression of osteopontin correlated with progression. The colon cancer study linked above did not do serum levels.
The typical mesothelioma case has a median survival of at most one year. There are cases of five year survivals in patients with early disease whose tumor were resected. Certaintly a means of detecting early disease would be welcome. The latency of mesothelioma is very longer, sometimes 30 or 40 years. OSHA has a mandated asbestos surveillance program but that program ends when the workers leave employment. In my experience consulting with a number of petrochemical companies over the past 25 years, most of the mesothelioma cases in refinery and chemical plant workers have occurred in retirees and most companies do not offer an exam program for retirees. The population to monitor and screen for early mesothelioma is the retiree group. On the other hand, pleural plaques in active employee exposed to asbestos in the years before the current OSHA standards were in place are not uncommon. The following issue will likely arise-should employees with pleural plaques be screened with serum osteopontin tests? Pleural plaques are not premalignant per se, that is a plaque is not transformed into a tumor. However, an asbestos exposed person whose exposure is signaled by a plaque is at risk of a mesothelioma. It may be that serial changes in the osteopontin level may be used in a similar manner to the PSA. The so-called PSA velocity may signal prostate cancer and perhaps serial increases in the osteopontin value may indicate early mesothelioma. Perhaps the utility of the test-if further data provides more validation-would be in periodic measurements in retirees with pleural plaques.