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Why the critics of screening mammography are wrong

Why the critics of screening mammography are wrong

Mammography screening is one of the major medical successes of the past several decades, yet this fact seems unable to break free of the doubts promulgated by such articles as Dr. Leonard Berlin's, published in an issue of Diagnostic Imaging earlier this year (“Disagreement continues to dog screening mammography,” April, page 31). I suspect that few people are aware of the fact that the death rate from breast cancer, the second leading cause of cancer deaths among women, has decreased by almost 30% since 1990. This is a remarkable achievement, especially in light of the fact that the death rate had remained unchanged for the preceding 50 years.

The statistically significant mortality reduction in the randomized, controlled Two County trial of mammography screening in Sweden1 led to the onset of widespread screening in the U.S. This initiation of nationwide screening led to a sudden increase in annual breast cancer incidence in 1984-85. The sudden decrease in cancer deaths that began in 1990 is clearly related to the preceding, equally sudden, increase in earlier cancer detection.2 Although oncologists, citing computer modeling, would like to claim that improvements in therapy are responsible for the decline in deaths,3 studies in Sweden4,5 and the Netherlands,6 using direct population data, have shown that at least two thirds of the decrease in deaths is due to mammography screening (this result is also shown in Berry's computer model, but it has been ignored by opponents of screening).

I am unaware of any test that has been as completely studied or challenged and has so successfully met the challenges as mammography screening. Three steps are required to prove that a screening test for breast cancer is efficacious. The first is that it must be able to detect breast cancers at a smaller size and earlier stage than is possible without the test. The Breast Cancer Detection Demonstration Project (BCDDP) in the 1970s proved this.7 The second is that randomized, controlled trials must show the test brings about a statistically significant reduction in mortality. Such a decrease in deaths has been clearly demonstrated by the seven randomized, controlled trials of mammography screening.8 The third is that when the screening test is introduced into the general population, the death rate declines. Mammography has fulfilled all three requirements.

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