The problem with cancer is that by the time it is detected, it is usually fairly advanced, and therefore difficult to treat. If it could be picked up earlier, this would increase the chances of successful treatment. Although cancer is the second leading cause of death in the US, the only FDA-approved tumor marker test for early detection is the PSA prostate cancer blood test. But it doesn't actually work very well. For one, levels of PSA estimate the likelihood that a man has prostate cancer, but does not provide a definite answer. Second, PSA is not cancer specific. The protein is produced in those without cancer as well as with it; and other conditions such as benign prostatic hyperplasia and prostatitis can cause a borderline or high PSA result. Lastly, when cancer is detected, it's often in cancer patients whose tumors are too large to be treatable.
Despite these drawbacks, the US market for PSA (developed by Hybritech Inc. , now part of Beckman Coulter Inc. ) is worth over $200 million annually; but with...