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Breast cancer math.

November 24, 2009

The latest recommendation from a US task force is that women don’t need regular mammograms until age 50.  The old recommendations were to start at age 40.  The USA Today article provides a number of statistics for risk of death from breast cancer.  When stats are given as a percent, I like to extend it out to an actual number.

MAMMOGRAMS, RISK OF DEATH
Mammograms reduce the risk of dying from breast cancer by a fraction of a percent, research shows.10-year risk of death from breast cancer:

Ages
40-49
Ages
50-59
Without screening 0.33% 0.89%
With screening 0.28% 0.69%
Absolute reduction in risk 0.05% 0.20%

Source: Steve Woloshin, Veterans Affairs Outcomes Group

Of 10,000 women aged 40 to 49, 33 are expected to die within 10 years from breast cancer.

If those same 10,000 women had screening, 28 would be expected to die within 10 years from breast cancer.

Of 10,000 women aged 50 to 59, 89 are expected to die within 10 years from breast cancer.

If those same 10,000 women had screening, 69 would be expected to die within 10 years from breast cancer.

So, screening 10,000 women aged 40 to 49, would save 5 lives and screening 10,000 women aged 50 to 59 would save 20 lives.

BUT if the 10,000 women aged 40 to 49 are screened annually for 10 years, 5,000 would have a “false alarm” at least once and many would undergo investigations because of that false alarm.

Basically, screening all women aged 40 to 49 is not cost effective.  Individual women with other risk factors, especially a family history, should be screened early and often.  That is a much more effective use of resources.

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