Tuesday, March 20, 2012

Diagnosing cancer: Blissful ignorance

MEN in America, Europe and other developed regions of the world have a 16% chance of being diagnosed with prostate cancer at some point during their lives—and yet they have only a 3% chance of dying from the disease. Despite the statistics, an industry has grown up around treating prostate cancer which, in most cases, would be best left well alone. The problem is finding the few instances where the cancer is aggressive enough to spread. Unfortunately, lacking better diagnostics, 48 men have to be needlessly treated—at considerable discomfort and possible change in lifestyle for the worse—so that one man’s life may be spared.

The widely used PSA test has been criticised for giving too many false-positive results, which, in turn, lead to over-treatment of cancers that might never have caused harm. Among men with PSA levels in the warning zone (between four and ten nanograms of PSA per millilitre of blood), biopsies show that over two-thirds of them had no trace of prostate cancer. Meanwhile, one in six men with PSAs in the normal zone (below 4ng/mL) were subsequently found to have been harbouring cancer cells in their prostate glands.

Usually a family doctor will refer a patient to a urologist if his PSA level is above 4ng/mL—or if the level rises by more than 0.35ng/mL over the course of a year. Because of the vagaries of the PSA blood test, many urologists confronted with borderline cases have started using a biomarker in the urine that focuses on a gene called PCA3. Comparing the activity level of the PCA3 gene with that of the PSA gene can be twice as accurate as relying on a PSA test alone. Based on such findings, the urologist may recommend a biopsy.