Breast cancer deaths drop—but not because of mammography

Mammography screening is usually credited with the drop in breast cancer deaths recorded in many countries, including the U.S.  But a case is building for improvements in breast cancer treatment as the most likely cause. The decrease in deaths has occurred in many European countries that did not start  mammography screening until the 1990s, which happens to coincide with greater use of long-term adjuvant therapy (e.g., tamoxifen, chemotherapy) given after the initial treatment is over.  Researchers say the case for adjuvant therapy is made stronger by the fact that,  in some of these countries, the greatest decreases in breast cancer deaths were among young women (under 50), the age group that never received mammography screening.

As someone who has followed the “selling” of mammography screening to American women that started in the early 1970s, I offer some background for the new findings from Europe. Thanks to nearly 50 years of research, we know more about mammography than any other cancer screening test. Expert panels with no conflict of interest have concluded that the breast cancer mortality rate among mammography-screened women (in randomized trials) is only 16% lower than that of unscreened women. In the U.S., there was no reduction in breast cancer deaths until the early 1990s and about 2% a year thereafter.

Today, there is a greater understanding of cancer. Some abnormalities that look like cancer under the microscope do not become invasive, if left untreated. Many regress spontaneously, stay put, or grow so slowly they will never make their presence known.  At least as far back as the 1970s, pathologists knew about these non-progressive cancers that can occur in all major organs of the body.  But women weren’t hearing from them.  Instead, radiologists and surgeons dominated the promotion of mammography screening in the early years. Today, it is the radiologists who are often quoted in the media, warning us about the dangers of forgoing mammography screening while downplaying its harms.

Well, it is quite reasonable for women to forgo screening—that is, after becoming well-informed. Here are the highlights of several review articles published in the last few weeks.  See below for my sources.

• There are usually dramatic increases in the discoveries of new breast cancers after mammography screening takes off. Tomorrow’s cancers are found today is the standard explanation.  This  ignores the fact that in every major randomized trial, some of the regularly screened women—who have had many previous “all-clear” mammograms—are nonetheless diagnosed with  invasive tumors that are fatal despite prompt treatment.  Recent studies conducted in many countries, including the U.S., show that mammography screening has not reduced the occurrence of large invasive cancers.

• The aforementioned large increase in new cases of breast cancer without a large decrease in the rate of new cases of advanced cancer (over time) indicates that much of the increase is due to detection of non-progressive cancers (i.e., overdiagnosis). Here’s how the Cochrane review on mammography screening assessed the damage: “For every 2,000 women who are screened throughout 10 years, one will have her life prolonged. In addition, 10 healthy women, who would not have been diagnosed if there had not been screening, will be diagnosed as breast cancer patients and will be treated unnecessarily.”

• Women are often told that mammography-detected breast cancers require less drastic treatment.  The opposite is true. Mastectomy rates were going down in some European countries in the years prior to the introduction of mammography screening but went up afterwards. Many countries, including the U.S., show 20% more mastectomies in the screened women compared to the unscreened women. One factor is the large increase in the detection of ductal carcinoma in situ, or stage 0 breast cancer, which was rare in all countries prior to the introduction of mammography but is now a common diagnosis.  DCIS  is treated increasingly with mastectomy, though it has long been known that only about 20% to 30% of DCIS will go on to become invasive breast cancer if left undetected, according to Susan Love, MD, author of Dr. Susan Love’s Breast Book.

• Physicians at the Dartmouth Institute of Health Policy addressed a common misconception about mammography in a paper published online in Archives of Internal Medicine (see below). “The presumption often is that anyone who has had cancer detected has survived because of the test, but that’s not true,” according to co-author H. Gilbert Welch. “In fact, and I hate to have to say this, in screen-detected breast and prostate cancers, survivors are more likely to have been overdiagnosed than actually helped by the test …  It’s important to remember that of the 138,000 women found to have breast cancer each year as a result of mammography screening, 120,000 to 134,000 are not helped by the test.”

Maryann Napoli, Center for Medical Consumers©

Related post
There is aid for breast cancer patients who must decide about adjuvant therapy.  read more

Sources for above post
“Why mammography screening has not lived up to expectations from randomized trials.” Cancer Causes Control, published online November 10, 2011.  This is the source for virtually of the above.  Click here

Cochrane review that assessed the harms as well as benefit of mammography screening.  Click here   Want to know more about the Cochrane Collaboration?   Click here

“Likelihood that a woman with screen-detected breast cancer had her ‘life saved’ by that screening” Archives of Internal Medicine, published online October 24, 2011.  This is the source for the last bullet point.  click here    Better yet, Click here for an easier to read New York Times article about this study.  Added December 4, 2012:  YouTube vide0 explaining a new study that found mammograpy screening accounts for overdiagnosis and overtreatment of 1.3 million American women over the four decades since it was first introduced.