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Swedish study questions mammography screening programmes

Susan Mayor , BMJ

Analysis of the outcome of mammography screening in Sweden over the past 10 years has shown no significant reduction in mortality from breast cancer.

The study analysed data from 17 county councils in Sweden that introduced mammography screening in the late 1980s. The results showed an overall reduction in breast cancer mortality of 0.8%when the number of observed deaths was compared with those expected during the period 1986 to 1996 (L kartidningen 1999;96:904). More than 600000 women aged 50 to 69 years were included in the study.

A member of the research team, Dr Gïran Sjïnell, a general practitioner in Stockholm, commented: "Our main finding was surprising-10 years' observation in a huge population of women undergoing screening showed no sign of a reduction in mortality from breast cancer." He contrasted this with clinical trials supporting screening, showing up to 30%reductions in mortality. "We think that the findings illustrate the difference between trial conditions and real clinical practice. Perhaps the trials included slightly different populations or may have been stopped after significance had been reached, failing to look at longer term effects."

The researchers warned that the screening programme had led to considerable numbers of women being given a false positive diagnosis and undergoing unnecessary biopsy. Nearly 100000 of the women in the study had received a false positive diagnosis. Of these, approximately 16000 had undergone biopsy, and more than 4000 women underwent breast surgery, including mastectomy. "Women should be warned about the potentially negative consequences of screening," suggested Dr Sjïnell. He pointed out, however, that the new research does not in any way question the use of mammography for diagnosing breast cancer.

Other breast cancer screening specialists have argued that breast cancer screening is worth while. Michael Dixon, an honorary senior lecturer at the Edinburgh Breast Unit, Scotland, said: "The science for mammographic screening for breast cancer is very sound. In fact, the new findings are easily explainable. Experience elsewhere has shown that there is a long lag between initiating a breast screening programme and reaching a level of detection that will reduce mortality." He explained that radiologists taking part in trials of mammography screening-which have shown high rates of breast cancer detection-are generally highly skilled and experienced. "When screening is opened up to national programmes a much larger population of radiologists is involved. Inevitably, it takes some time for them to climb up the learning curve in accurately detecting abnormalities," said Mr Dixon.

The national coordinator for the NHS Breast Screening Programme, Julietta Patnick, agreed: "Last year was the first year that we matched the UK national breast screening programme matched trial results in detecting cancers. This took nine to ten years to achieve."

After 10 years of mammography, breast cancer deaths were not reduced