The latest report from a long-term Canadian study into breast cancer screening suggests it isn't reducing the number of women who die from breast cancer.

The study looks at the impact of screening mammography on cancer rates and deaths to cancer in women aged 40 to 59 who were followed for nearly 25 years.

There were more breast cancers detected in the women who underwent screening as compared with women whose breasts were checked for lumps by a medical professional.

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Still, the numbers of women who died from breast cancer in the two groups were virtually identical, suggesting mammography found some cancers that didn't need to be treated.

Lead author Anthony Miller of the University of Toronto says for him and his co-authors the message is clear: the use of mammography to screen for breast cancer ought to be rethought.

The Canadian Cancer Society disagrees, saying that there is other evidence supporting breast cancer screening in women over the age of 50, and the American College of Radiology and Society of Breast Imaging says the study is misleading and incredibly flawed.

In a statement, that group – which represents radiologists, the professionals who read mammograms – reiterates complaints about the study that it has been making for years.

It alleges that the researchers knew which women already had cancer and steered them into the mammography arm of the trial to skew the results. In also suggests the mammography was of poor quality, saying the machines used were secondhand and not state of the art.

For a randomized controlled study to produce valid results, the people in the two arms of a trial must be essentially similar. Stacking one arm of the trial with more sick people would have an impact on the findings.

Miller has heard many of these critiques of the Canadian National Breast Screening Study over the years, and he dismisses them in short order, calling them "misconceptions and I really must say they're falsehoods because they're saying things that are not true."

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The claim the mammography machines were secondhand was a new one, though, he says.

"Absolutely wrong. I don't know who on Earth invented that one," Miller says, adding of the radiologists, "they're obviously conflicted."