If the hype is right, then finding a tumor when it is small should mean a better chance that surgery, radiation and/or chemotherapy will eradicate it, allowing you to live until something else kills you. Early detection should produce clear, unquestionable benefits.

Yet it doesn’t. Not the PSA [for prostate cancer], not early detection of lung or testicular or pancreatic cancer, or glioblastomas, a type of brain cancer. Even mammography is iffy, since trials showing a decrease in mortality were done before the age of adjuvant therapy. Colonoscopy might cut mortality, but it has never been tested in a randomized, controlled trial….

If the failure of most early detection to strongly affect whether you live or die makes no sense to you, you’re not alone. “The medical community has done such an extraordinary job getting out the message that early detection is tantamount to cure, it’s incorporated into people’s bone marrow,” says [Barrett] Kramer, [associate director of disease prevention at the National Institutes of Health ].

For decades, women have heard that the best hope of curing breast cancer is finding it early. To that end, doctors have taught women about the importance of three breast cancer screening techniques: breast self-exam, clinical breast exam (a breast exam done by a health professional), and mammography. This emphasis on breast cancer screening has perpetuated the belief that all breast cancers can be cured if they are found early. It also leads people to believe that all women who survive breast cancer do so because their cancer was found early.

The latest research, however, indicates that neither of these beliefs appears to be true. It now looks like there are about six different types of breast cancer that vary in how aggressive they are. Some of them are so "good" that they will never metastasize (spread throughout the body). And that means it doesn't matter when you find them. They just don't have the ability to cause someone to die of breast cancer. Others are very "bad" and so aggressive that no matter when you find them — which means even if you find them when they are still very small — they have already begun to wreak havoc. These are the types of cancers that cause women to die of this disease. Still others, probably about 30 percent, have the potential to become "bad" if not stopped early. These are the cancers whose outcomes are affected by breast cancer screening programs and early detection. These are also the cancers mammography is best at finding.