The screening myth and war on cancer

• Published date: 15 November 2014
• Publication title: Gulf Times

Breastcancer screening has long been viewed as one of the most important tools for reducing mortality from the disease. That is why recent doubts about its effectiveness intensified by the publication in February of the 25year followup to the Canadian National Breast Screening Study have come as such a shock.

How can breastcancer screening, which facilitates early detection of the disease, not prevent deaths from it?

Understanding screening's limitations requires, first and foremost, an understanding of the process. A mammogram (Xray of the breast) is administered to ostensibly healthy people to detect unsuspected disease. If any abnormalities are found, a diagnostic test is conducted to confirm the presence of the disease.

If the results are positive, treatment begins.

The first limitation of breastcancer screening is obvious: where effective diagnosis and treatment are not available, screening cannot have any impact. But there is more to the issue namely, whether screening ultimately fulfils its intended purpose of reducing breastcancer mortality rates.

There have been several attempts to evaluate, through observational studies, the impact of screening in the general population. But such studies, which are based on comparisons between uncontrolled groups, tend to produce biased results. None has been able to account for differences in treatment.

More important, none has found a reduction in advanced breast cancer in the screened groups a requirement to deem screening effective.

With observational studies producing inadequate results, scientists turned to a procedure developed years ago to evaluate new tuberculosis drugs: randomised screening trials. Such trials begin with the selection of women at risk of developing breast cancer, and randomly allocate them to be screened or not.

Any woman in either group who develops breast cancer is treated to the fullest extent possible, following the closest possible treatment plan to other participants in the trial (taking into consideration the stage of the disease at diagnosis).

Researchers follow the women's progress over many years, with the goal of comparing the two groups' mortality rates.

In North America, where, for ethical reasons, randomisation requires informed consent, only two such trials have been conducted. The first was in New York in the 1960s, using annual mammograms and breast examinations for the screened group.

The second, the Canadian National Breast Screening Study, which began in the 1980s, also...