In Edinburgh, 45,000 women were entered into a randomized trail of breast cancer screening by mammography and clinical examination. After seven years of follow up the death rate was reduced by 17 percent, but in women over fifty this rose to 20 percent. This is still not considered to be a statistically significant reduction in the death rate.

The researchers concluded that, "The Edinburgh mortality data lack statistical power and are consistent either with no reduction in mortality or a reduction of over 30 percent. Longer follow up is required to establish which, and we will report further after 12 years of follow up."

Between 1979 to 1981 a non-randomized trail was started on women age 45 to 64 living in eight different locations in the United Kingdom. Nine years into the study, the reduction in breast cancer death rate was about 20 percent, falling just short of statistical significance.

The National Breast Screening Study In Canada

For 12 years, leading breast cancer experts have been waiting for the outcome of a large well designed Canadian study that began in 1980. The National Breast Screening Study studied 89,000 women in 15 centers across Canada. The study was designed to definitively answer questions about whether physical exam plus mammography decreases the death rate from breast cancer in women 40 to 49 years and whether mammography contributes over and above physical examination to the detection of breast cancer in women age 50 to 59 years.

The NBSS is the largest individually randomized study to date evaluating breast screening among women aged 40 to 49 years. The researchers found that although the combination of yearly mammography and physical exam detected more and smaller breast cancers than in the unscreened group, there was no impact on the annual breast cancer death rate at the seven year mark. In fact, there were more deaths in the screened group than in the unscreened group (38 versus 28), although this was not statistically significant.

The NBSS study is the only study so far to evaluate the value of mammography, over and above physical exam in women 50 years or older. The researchers found that although more cancers were detected in the group getting mammograms and physical exams, the breast cancer death rate was the same for both groups. This may mean mammography detects non-fatal cancers, or it may mean it is too soon to see any benefit from mammography screening.

Some radiologists, and some physicians involved in the British Columbia Cancer Control Agency's project to screen women aged 40 to 49 in that province, maintain that NBSS results are invalid because the quality of mammography early on was less than desirable. Some of the radiologists criticising the study were among the fifty who were reading mammograms for the NBSS.

Dr. Anthony Miller, has countered the accusations saying (CBC radio, Nov.21/92), "we used what was available in Canada at the time. We used the experts that we could find. If they regarded their training as being inadequate, they certainly never told us so."

In fact, as Dr. Anthony Miller and Dr. Cornelia Baines, told The Medical Post (Jan.5/93), "All NBSS radiologists were certified and based in either teaching hospitals or provincial cancer centers; were expert diagnostic mammographers; received feedback from the reference radiologist, and had an opportunity for upgrading their skills at meetings."

Dr. Antoni Basinski, from the Institute for Clinical Evaluative Sciences at Sunnybrook Hospital in Toronto, states in his article in the CMAJ (Nov 15/92). "Suboptimal quality (of mammograms) may be expected to diminish the size of a potential effect but not abolish it... The NBSS investigators appropriately addressed internal quality control and took measures to improve quality where necessary."

Moreover, as Dr.Cornelia Baines points out the mammograms done in the first two years of the study, when there was the most problem with mammogram quality, only comprise 2.5 percent of the total mammograms done.

Dr. Vivien Basco, chairman of the Policy Advisory Group to the NBSS, and ironically an outspoken critic of the study, said in a CBC radio interview(Nov/92). "The quality of the mammograms in NBSS was almost certainly as good as the ordinary mammography being done in the country at the time, or for that matter in the U.S. but not up to the standards of expert mammography clinics."