Even when such simple self-examinations are performed conscientiously, they can detect only tumors large enough to feel, which are therefore already somewhat developed. About 80 percent of breast lumps are not cancerous. Early detection increases survival rates for some cancers dramatically. If all melanomas were detected while still small and confined to one area, the cure rate could approach 100 percent. Three-fourths of colon or rectal cancer patients could be saved by early detection.
Shields works on devising tests to determine who is at increased risk of developing a cancer.
He studies oncogenes, which in many cases started as normal genes regulating cell growth. Suppressor genes, which inhibit cell growth, oppose oncogenes. By comparing these genetic variations in people not afflicted with cancer and in those who are, he tries to find which factors may predispose individuals to cancers. The field is called biochemical epidemiology, and we are specifically interested in things that happen to your genes that would increase your risk of cancer. Heredity, lifestyle and environment are all factors in the search.