Canadian Press
November 24, 2008
TORONTO -- A significant portion of invasive breast cancers may regress on their own without treatment, a new study that is bound to provoke controversy suggests.
The study, published Monday in the journal Archives of Internal Medicine, suggested breast cancer screening may be leading to over diagnosis of cancer, with about 22 percent of cases likely to resolve themselves without treatment.
Once a breast cancer is found, however, it wouldn't currently be considered ethical not to treat. So - if the theory is correct - large numbers of women may be having surgeries, radiation, chemotherapy and other treatments that would never have been needed if their cancers hadn't been detected.
"If we are right, then this is a kind of paradigm shift," said lead author Dr. Per-Henrik Zahl, a senior statistician with the Norwegian Institute of Public Health.
Zahl, who admitted he has been trying to get the study published for about four years, said the risks of over diagnosis of breast cancer are real.
Radiation can damage the heart and coronary arteries. A previous randomized controlled trial showed that about one in 10 women who receive radiation for breast cancer will die from heart damage attributable to it, he said.
In an interview from Oslo, Zahl said that if he and his co-authors are correct, two women would end up dying from complications of breast cancer treatment for every woman saved by screening.
"And that's a very bad trade-off."
The findings are likely to spark heated debate. Zahl acknowledged several journals refused to publish the study before it was accepted by Archives of Internal Medicine, a journal published by the American Medical Association.
But an editorial in the journal stressed that the findings are consistent with several observations about breast cancer that have troubled investigators for years.
And the editorial's authors, Dr. Robert Kaplan of the UCLA School of Public Health and Dr. Franz Porzsolt of Germany's Clinical Economics University of Ulm, said the hypothesis of breast cancer regression, while counterintuitive, is "difficult to rule out."
"We know from autopsy studies that a significant number of women die without knowing that they had breast cancer," they noted.
In what is described as an "elegant" study design - high praise among scientists - Zahl and his colleagues used the introduction of a breast cancer screening program in Norway to explore the question.
They compared breast cancer rates among nearly 120,000 women who had three rounds of mammography between 1996 and 2001 to those among nearly 110,000 women of the same age range (50 to 64) in the five-year period preceding the start of the breast cancer screening program. Those women, known as the controls, had one mammogram.
In statistical terms, the two groups of women were identical. Their educational profile was closely matched, they had roughly the same average family income and the same average number of children. So the rates of cancers in the two groups should have been equal.
In fact, the women who hadn't been regularly screened had 22 per cent fewer breast cancers. The authors explore a number of arguments about why that might be - noting for instance that use of hormone replacement therapy jumped during the second period studied.
But the authors conclude none of the potential other explanations they explored could account for such a large difference between the two groups.
"All the caveats that could be explored have been explored in terms of accounting for the things that people would call were weaknesses (of the study)," agreed Dr. Cornelia Baines, a professor in the University of Toronto's school of public health and co-principal investigator of a landmark study into mammography, the Canadian National Breast Screening Study.
Baines, who has breast cancer that was missed by mammography, said the findings are important.
But she said it is currently not possible with most breast cancer diagnoses to know which ones are likely to be lethal and which might indeed regress if Zahl and others who share his views are correct.
"The incontrovertible truth is that once you've screened a woman and you find an abnormality, you have to biopsy," she said.
"If you biopsy, you have to follow through with surgery if the biopsy reveals malignant tissue. You can't stop that. You can't say: 'Well, I've been screened and there is a chance that this is over diagnosis.' You can't do that."
Finding ways to answer the questions raised by the study will be difficult, experts say.
But in the meantime, Baines said, this study may serve as an important reminder to women and the medical community.
"What is important and it seems to me it's been ignored for a long, long time is that...screening doesn't only have upsides. It has downsides," she said.
"And if women want to accept the downsides and proceed with screening, then that's great. But I personally believe that they should only make that choice when they are fully informed. And a lot of them have not been fully informed about the over diagnosis scenario."
The Canadian Press, 2008
