Although we all would like to think that public health pronouncements are the unmitigated truth about any issue, rarely is that the case. We can only give our best guess, based on the current available data and our current understanding of the disease. Luckily, research continues, hypotheses are reformulated and new recommendations are made.
The path to the truth in science and medicine is nonlinear. Sometimes clinical practice gets ahead of the data and has to be pulled back. This is what happened with post-menopausal hormone therapy when the large Women's Health Initiative trial demonstrated that the then-common practice of giving women hormones at menopause was causing more harm than good. How big was the harm? We know that after the report came out, many women abruptly stopped taking their hormones, and that year, the incidence of breast cancer went down 15%.
We saw a similar shift in women's health when highly touted and extensively used high-dose chemotherapy with stem cell rescue as treatment for aggressive breast cancer was found to not only be no better than the regular-dose chemotherapy we had been using, but to have significantly higher side effects.
I present these examples in an attempt to put the controversy regarding the new mammography guidelines into perspective. The shift in guidelines is not a conspiracy of the insurance companies or the government. It is pure coincidence that they came out while we are in the throes of the healthcare reform debate.
The U.S. Preventive Services Task Force was formed to periodically review the available data and come up with the best recommendation. A lot has changed since its last recommendations in 2002.
One key shift has been in our understanding of the biology of breast cancer. We used to think there was just one kind of cancer that grew at a steady pace; that when it reached a certain size, it spread to the rest of the body. As a result, it seemed to make sense that we could save lives if a screening test could identify the cancer while it was still "early," before it had spread. That's how we developed the notion of early detection. And it works, sometimes.
In the best of hands, mammographic screening in women over 50 will reduce a woman's risk of dying from breast cancer by 30%. That is a lot, but it is not 100%. Why? It turns out that breast cancers are not all the same. There are at least five kinds, with different growth rates and levels of aggression. Some are so aggressive that they will have spread before they are visible on a mammogram or form a lump. Some are very slow growing or may not even have the ability to spread, so there is no benefit from finding them early. This is because of the biology of the disease, not the limitations of screening.
One of the reasons that mammography is a less effective tool in young women is that they have a higher rate of these aggressive tumors. Younger women also have breast tissue that is more sensitive to the carcinogenic effects of low-dose radiation. Calculations by a research team in Britain published in the British Journal of Cancer in 2005 suggest that it is possible for women to develop cancer because of the cumulative radiation from yearly mammograms starting at 40 or younger. Finally, mammograms are generally less accurate in younger women who have dense breast tissue, which can mask a cancer. Thus the balance of risk versus benefit is not as clear.
Since the 2002 task force guidelines were released, there has been new data from Britain, which was the first study to look at whether there was any benefit to having women start mammography at age 40. The researchers have followed women in this study for more than 10 years, which means they are now over age 50. To date, they have not shown a statistically significant decrease in mortality. This means if there is a benefit, it must be very small.
The new guidelines are based on this information. They do not say that no women under 50 should get mammograms, but that we should not routinely screen women under 50. Less noted by the media, the guidelines also recommend that we not routinely screen women over 75, where the benefits are dependent on the woman's life expectancy. In both cases, a woman will need to review her situation with her physician.
This has left many young women confused and asking how will we find our cancers if we don't have mammograms. The alternative to mammographic detection of cancer is not death. The alternative is that a woman will find a cancer herself or her physician will find it. The normal "poking around" that women do has been found to be just as good at finding breast cancer as a monthly self-exam.
That's why the task force recommended that doctors encourage women to be familiar with the look and feel of their breasts but to stop teaching formal breast self-exam.