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Annual mammography from age 40 doesn't lower breast cancer mortality

Does starting annual mammography at age 40 decrease breast cancer mortality?

Does starting annual mammography at age 40 decrease breast cancer mortality?

Synopsis

Women in England, Scotland, and Wales aged between 39 and 41 were randomly assigned to annual mammography (n=53,884) or usual care (n=106,956).

The research team evaluated the women until they were 48 (mean follow-up = 10.7 years; more than 99 per cent accounted for).

The main outcomes, breast cancer mortality and all-cause mortality, came from the NHS Central Register and were analysed via intention to treat.

Overall, 81 per cent of the women had at least one mammogram and screened women had, on average, 5.6 mammograms during the study period.

The authors state, but give no data, that their evidence indicates the extent of screening in the control group is small.

During the study, the cost of screening in this age group was not covered by the NHS and would therefore be borne at personal expense.

At the end of the study, the differences between groups in all-cause mortality (1.66 versus 1.72 per 1,000 person-years) and breast cancer mortality (0.18 versus 0.22 per 1,000 person-years) were not statistically significant.

However, the study was originally designed to have 80 per cent power to detect a 20 per cent relative reduction in breast cancer mortality. But the study group ran out of money and did not recruit as many women as they had planned.

The final study had 72 per cent power. In other words, although this was a well-conducted study, the statistical aspects are limited.

For example, compared with usual care, we would need to screen 2,512 (95 per cent CI, 1,149 - 13,544) to prevent one breast cancer death over 10 years.

Level of evidence

1b (see www.infopoems.com/concept/ebm_loe.cfm)

Reference

Moss SM et al, for the Trial Management Group. Effect of mammographic screening from age 40 years on breast cancer mortality at 10 years' follow-up: a randomised controlled trial. Lancet 2006;368:2053-60.

Bottom line: This study found that 10 years of annual mammography starting at age 40 produced no statistically significant reduction in breast cancer mortality.

The screening of women in this age group is controversial and the limitations of this data will not settle the arguments.

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