Formula Predicts Cancer Risk

Mayo Clinic doctors say they have developed a formula for telling the difference between prostate cancers that require surgery and those that grow so slowly they can safely be left alone.

The system involves mathematically combining four factors: the size of the tumor; how malignant its cells appear to be under a microscope; the speed with which the tumor is growing; and the patient’s age.

Prostate cancer is the second leading cause of cancer deaths among men, after lung cancer.

About 317,000 American men will be diagnosed with prostate cancer this year, and 41,400 will die of it, the American Cancer Society estimates.

Improvements in detecting prostate cancer have led to much higher rates of diagnosis in recent years, but that has created a problem:

Prostate cancer usually occurs in older men and often is slow-growing. Though 30 percent to 40 percent of men over 50 have prostate cancer, only 8 percent of such cases cause problems before the men die of other causes.

For many men, it makes more sense to leave the cancer untreated than to risk surgical complications such as urinary incontinence or impotence. But science is inexact in predicting which cancers will spread or cause problems such as blocking urine or semen.

The study was reported in today’s issue of The Journal of the American Medical Association.