One-third of breast cancers that show up on mammograms may be essentially harmless, meaning that treating every tumor causes unnecessary trauma, a five-nation study suggests. A mammogram doesn't reveal whether a cancer is lethal or harmless, so all get treated when some could be merely monitored, the BBC reports. The finding means "that screening for cancer, in this case breast cancer, is a much closer call than has been previously advertised," writes a Dartmouth researcher.
"It has the opportunity to help some women but it also has the consequence of leading others to be treated needlessly for cancer and that's not a trivial thing," he argues in the British Medical Journal. The five nations in the study were Australia, Britain, Canada, Norway, and Sweden.