Why Have Breast Cancer Rates Decreased?

The number of U.S. women diagnosed with breast cancer dropped in 2003, according to researchers from the University of Texas-M.D. Anderson Cancer Center. The reasons are yet unknown, but there are a few speculations. In mid-December 2006, at the 29th Annual San Antonio Breast Cancer Symposium, the Texas-M.D. Anderson researchers presented data that the incidence of breast cancer fell by 7% in 2003. This translates to 14,000 women who might otherwise have been diagnosed with breast cancer.

The media was quick to interpret this finding as proof of a connection between women’s hormone use and breast cancer. Here is the thinking: In July 2002 the Women’s Health Initiative (WHI) study on combined estrogen and progestin treatment in postmenopausal women was stopped prematurely, due to fear that this type of treatment would cause an increased risk of heart attack, stroke, blood clots, and breast cancer (see my recent article on this topic). . Understandably, many women became fearful of taking any hormones for menopausal symptoms, and many of them stopped taking hormones altogether. So the new finding of the drop in the incidence of breast cancer in 2003 has been interpreted as yet another proof that hormones cause breast cancer.

It is prudent to be cautious in order to avoid drawing premature conclusions. The very first question that comes to mind is how stopping hormones in late 2002 could have an effect so quickly – in just one year. We really need to wait until the breast cancer incidence for 2004 and later is known before we can take a look at the larger picture and begin to draw any conclusions. Even the Texas-M. D. Anderson researchers themselves state that “…because the analysis is based solely on population statistics,” they cannot know for certain the reasons why incidence declined. “We have to sound a cautionary note because epidemiology can never prove causation,” one of the researchers says. They considered whether other effects may have been involved (such as decreased use of screening mammography and changes in the use of anti-inflammatory agents, SERMs, or [cholesterol lowering] statins) but only the potential impact of HRT was strong enough to explain the effect (see the below link to the news release).

Even if the decline in hormone use is involved, it is unlikely to be the only reason why fewer incidences of breast cancer were diagnosed in 2003. What are some of the other possible explanations?
– SERMS (Selective Estrogen Receptor Modulators) such as raloxifene are used to treat osteoporosis. Raloxifene lowers the risk of breast cancer in women who take it to treat osteoporosis. From 2001 to 2003 raloxifene use increased by 12%.
– Mammograms fell by 3% in 2003 among 50-64 years old (Parker-Pope). This may have resulted in fewer incidences of breast cancer being detected and diagnosed that year.
– Both calcium use and the use of anti-inflammatory drugs have been linked to reduced breast cancer risk. From 2000 to 2003, calcium use went up by 40%.
– The use of anti-inflammatory drugs more than doubled from 1999 to 2003.
– Finally, women may have been less inclined to see their health provider for annual checkups after the WHI scare, potentially resulting in fewer diagnosed incidences of breast cancer.

All of these factors should be considered as possible reasons for the decline in breast cancer incidence. Obviously, more research is needed before we can say for sure what caused the incidence to drop and whether the decline is a permanent trend.

References
The decline in Breast Cancer Cases Likely Linked to Reduced Use of Hormone Replacement. M. D. Anderson News Release 12/14/06

Tara Parker-Pope (December 15th, 2006) What Made Breast Cancer Decline in 2003? The Wall Street Journal; B1, B2

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