A NEW report raises fresh questions about the value of mammograms.
THE rate of cancers that have already spread far beyond the breast when they are discovered has stayed stable for decades in the United States, suggesting that screening and early detection are not preventing the most dangerous forms of the disease.
The report, in Thursday’s New England Journal of Medicine, comes a week after the American Cancer Society advised most women to start annual screening at age 45, not 40, and switch to every other year at 55.
The report’s lead author Dr Gilbert Welch said what, for the public, was “a very confusing debate” about screening, was really “a course correction”, prompted by more awareness of risks and benefits.
“Screening offers hope that cancer can be detected in an early, localised phase when it’s more amenable to treatment,” the study’s authors write.
But that assumes that cancer starts in one place, grows and then spreads. If that was always true, screening would reduce the rate of advanced cancers.
And that has not happened. The rate of breast cancers detected at an advanced stage has been stable since 1975, despite the wide use of mammography since the 1980s.
The average age of women diagnosed with cancer also has remained about 63, another sign that cancers are not being found sooner.
The trends suggest that some breast cancers are already “systemic”, or widely spread from the start, and that finding them sooner has limited impact.
Dr Barnett Kramer, a screening expert at the National Cancer Institute, said the report showed the limitations of mammography.
“I wouldn’t want to say it has had no effect, but it certainly has not lived up to the anticipated effect,” he said.
On the other hand, the authors write, the rate of advanced cases of prostate cancer has been cut in half since screening with PSA blood tests came into wide use around 1988, and the average age at which men are diagnosed has fallen from 72 to 70.
However, Dr Welch said, shifting the stage at which a disease was diagnosed was “only the first step for successful screening”, which also has to save lives to be worthwhile.
He said prostate or breast cancer screening was “a close call”, whereby “a few people are helped”, while many were harmed by false alarms that triggered unnecessary tests and treatments.