Researchers for the Swedish Two County study noted that in North America only one in every six to ten breast biopsies would be positive for cancer. The rate of false positives is much higher in North America than in Europe. In Sweden for example, if you have a breast biopsy, there is a 50 to 75 percent chance it will be cancer, whereas in North America, there is about ten to 20 percent chance it will be cancer.

• FALSE NEGATIVES: This means your mammogram shows up no sign of cancer, but there is a cancer. Women are thus falsely reassured and may delay seeking treatment. The percentage of false negatives is not known, but may be as high as ten to 15 percent, particularly in younger women.

Paradoxically, according to Dr. Baines, a false negative is more likely to occur with larger cancers.

In younger women, cancers can occur in the intervals between screenings, and these are usually fast growing cancers (about 20 percent of breast cancers). Mammograms are unlikely to be able to detect these kinds of cancer, which can sometimes double in size in 21 days.

• OVERDIAGNOSIS OF CANCER: Dr. Philip Prorok, Chief of The Screening Section of the National Cancer Institute, has stated that mass screening tends to detect mainly cancer in the dormant stage ("in situ" or "non invasive"). These cancers, he says, are known to be slow growing and have a better prognosis, screening or no screening. This means, according to Dr. Prorok, that screening programs have a built in bias to look as though they improve survival rates.

Fast growing breast cancers, which can double in size rapidly, are the ones most likely to be missed by screening, especially for women in the 40 to 49 age group.

Mammograms can detect cancers as small as one half centimetre (1/4 of a inch) Regular self exam can detect lumps at about one centimetre size (1/2 of a inch) But, says Prorok, "When a mammogram uncovers a very tiny tumour... it's not possible to know if it would have gone onto be a killing cancer, never surfaced, or even surfaced as a kind of cancer that could have even treated very well even at that point."

What Are The Critics Of Routine Mammography Saying ?

"If it should turn out that the type of cancer (fast or slow growing) is more important that the when it is diagnosed," says the Boston Women's Health Collective, "we will need to rethink our whole approach to cancer detection and treatment."

Dr. John Bailar III says that "virtually all experts conclude that an asymptomatic woman who is at least 50 years old will benefit from regular breast cancer screening by a combination of mammography and careful physical examination."

However, Dr. Bailar is opposed to screening for women under 50. Costs of screening, he says, "include not only the monetary costs, but also the anxiety, unnecessary biopsies, grave diagnostic delays from false negative reports, loss of faith in future screening examinations (and perhaps other medical care) resulting from the frequent false positive reports, and vigorous treatment of lesions that look bad under a microscope but are not life threatening, and would have been left alone in the absence of screening (JAMA, Mar.11/88)."

Dr. Charles Wright said in an article in the Medical Post (Feb.6/90). "Women are clamouring for mammograms because of the hype created around the benefits of mammography." He estimated that the Saskatchewan screening mammogram program would save the lives of five women per year at the cost of about 1.25 million dollars a year per life saved.

Dr. Wright wrote in Surgery (Oct/86) magazine. "On the positive side of the balance sheet there is a marginal reduction in deaths from breast cancer in older women... Negative factors include the false positive results leading to unnecessary operations, the false negative results that lead to an inappropriate reassurance, the raised level of anxiety in the female population and the tiny but real risk of radiation induced cancers."

At the 1988 annual meeting of The Irish College of General Practitioners, Dr. Skrabenek caused a furore when he claimed that screening had become a vast and profitable industry for radiologists.

Dr. Skrabenek said in article on medical ethics in The Lancet Medical Journal (May 21/88). "If individual "guinea pigs" must be protected from excessive research zeal by having to be informed about the inherent risks, the same imperative should apply with even greater force when whole populations of healthy people are put at risk by screening."