Chemical screening tests for the detection of cancers

For lunch, a couple of old biochemist friends from Harvard and MIT and I enjoyed Indian food just off Harvard square while discuss consulting strategies and new opportunities in biotechnology. The conversation drifted into new markers for cancer detection. Upon arriving home there was an Email from another consultant asking for advice on another cancer test. A number of such tests exist but few have value in screening the general population (PSA for prostrate cancer is an exception although even that test is criticised for too many false positives). Most cancer markers are chemicals that we all have but become elevated when cancer is present. The problem is that early cancer detection requires the measurement of low levels very close to the levels in people without cancer. This means that there is a high rate of false positives if the measurement is very sensitive as the levels seen in an early cancer are very close to the normal levels. The false positives are expensive to work up and cause unneeded concern. Once the cancer progresses the level will rise and is more easily distinguished from the normal levels. Many such markers have utility for following the course of the disease and the success of therapy. The overall problem is that cancer cells are normal cells that are dividing without proper control and contain no unique chemicals that can be used to unequivocally identify them.