Doctors routinely diagnose prostate cancer by measuring the amount of prostate-specific antigen (PSA), a protein produced by the prostate gland, in the blood, and by digital rectal examination (DRE). A higher-than-normal level of PSA indicates that something is amiss with the prostate, although it need not be cancer.

But PSA screening has a huge potential for error. DRE itself, riding a bicycle or sexual activity can temporarily increase PSA, resulting in considerable overdiagnosis of prostate cancer. In fact, in one study of 660 men who underwent prostate surgery, more than one-sixth of the non-palpable tumours diagnosed by screening were clinically insignificant and found not to warrant surgery after all (JAMA, 1994; 271: 368-74).

These newer tests can be used as a second opinion:

* The AMAS (anti-malignin antibody in serum) blood test, available from Oncolab Inc. in the US, and Quest Diagnostics in the UK, measures malignin, a blood molecule associated with malignant transformation of cells, and shown in more than 3000 double-blind studies to be raised in dormant cancer. The test is 95-per-cent accurate on first analysis, and up to 99-per-cent accurate on repeat analysis for the presence of any kind of cancer (Cancer Detect Prev, 1994; 18: 65-78; Int J Biol Markers, 1997; 12: 141-7).

* The free PSA test, which measures the percentage of PSA that is not bound to proteins in the blood. This test produces fewer false-positive results in those who don’t have cancer.