Mammogram Detection Rates
What is the detection rate for a single mammogram?
For a postmenopausal woman who does not take estrogen, a single mammogram will identify 85% of all breast cancers that would have been found by any means over the next 12 months, and 55% of all breast cancers that would have been identifiable over the next two years. For a premenopausal woman, a single mammogram will identify 65% of all breast cancers that would have been found by any means over the next 12 months, and 25% of cancers that will be found over the next two years. For women in the years surrounding menopause, and for those who use estrogen replacement therapy, the detection rates for a single mammogram fall between these figures.
Why are the detection rates different for older and younger women?
The difference in detection rates between older and younger women is partly due to differences in the density of the breast tissue, but mostly due to the different rates at which cancers grow. The hormone-rich environment of the breast tissue before menopause is favorable for tumor growth, if a cancer happens to be present. A cancer can double in size within six weeks to five months if a woman is 40, while the doubling time is between four and seven months if a woman is 60. This means that the length of time between "too small for a mammogram to spot" and "large enough for a woman to feel" is shorter for younger women than for older women.
How reliable are mammograms?
Mammograms aim to catch as many cancers as possible. However, mistakes occur, both in the form of false negative and false positive results. A false negative result occurs when a cancer exists but either doesn't show up on the mammogram film or the radiologist fails to recognize it as a cancer. A false positive result occurs when something on the mammogram leads the radiologist to think that a cancer exists, even when one does not.
