Does cancer screening save lives? Not nearly as many as you might guess

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Most people grossly overestimate the benefits of cancer screening, according to a new survey of 10,228 Europeans. A whopping 92% of women believe the life-expectancy benefit from breast-cancer screening is at least ten times bigger than it really is, or say that they don’t know how much benefit screening provides. (On average breast-cancer screening will save just one life for every thousand people screened, according to the study, published in the Journal of the National Cancer Institute.) Among men, 89% overestimate the benefit of prostate-cancer screening by a factor of ten or more, or say they don’t know how big the benefit is. (Prostate-cancer screening saves less than one life per 1,000 people screened, according to the study.)

In the U.S., in fact, the Preventive Services Task Force gives just a “B” grade recommendation to mammography, and it recommends against PSA prostate-cancer screening altogether for men over 75. In men under 75, the task force says there’s not enough evidence to issue a recommendation either way.

How is this possible? Mammography and PSA testing do both detect cancers effectively. But the question is whether catching a cancer early can really save lives, or whether the benefits of early detection outweigh any risks from the screening procedure itself. Mammography gets a B largely because it’s less useful in younger women (say, ages 40 – 49) than it is in older women, so that the task force believes that any benefit to younger women is quite minimal. (There’s good evidence, however, that screening at older ages can save lives.) With prostate cancer, however, it seems that the benefits of early detection just aren’t all that great in the best of cases — especially for older men. Early detection allows for treatment, of course, but treatments are often aggressive and unpleasant. An 80-year-old who discovers prostate cancer through screening and who doesn’t yet have symptoms, for example, is likely to die of something else before his cancer kills him. Serious cancer treatment may then only bring suffering, with minimal gain. And if screening doesn’t really help people to live longer, then it’s hard to justify all the unpleasantness of a screening test in the first place. A PSA test — or prostate-specific antigen test — is a simple blood test, nothing too intrusive. But screening does pick up false positives, which are typically then followed up with a biopsy, a much more invasive procedure that can have complications.

The best cancer screening procedures, according to the U.S. Preventive Services Task Force, are colorectal cancer screening for men and women over 50, and cervical cancer screening (pap smears) for sexually active women. Both procedures have minimal risks or side effects, while the benefit of early detection is well-proven. Both those procedures get an “A” grade.