The chances of a woman with screen-detected breast cancer surviving because of the mammography may be lower than previous estimates, researchers from Dartmouth Institute for Health Policy and Clinical Practice, Hanover, N.H., reported in Archives of Internal Medicine. The researchers used a model to estimate survival rates from breast cancer.
The researchers wrote:
“Today, more people are likely to know a cancer survivor than ever before,” the authors write. “Between 1971 and 2007, the number of cancer survivors in the United States more than doubled, from 1.5 percent to 4 percent of the population. Breast cancer survivors are particularly common: they now represent approximately 2.5 million, or one-fifth of the current survivor population.”
The authors suggest that there may be other possibilities that influence breast cancer survival, apart from screening mammography, despite very persuasive messages from women who emphasize that the test saved their lives.
H. Gilbert Welch, M.D., M.P.H., and Brittney A. Frankel created a model to estimate what the chances are that a woman with screen-detected breast cancer becomes a cancer survivor because of the screening. They used a National Cancer Institute software called DevCan in order to analyze data. They were able to estimate 10-year risk of diagnosis and 20-year risk of death. The model relies on two estimated possibilities for a female in the general population of the USA:
- The chances of having breast cancer detected thanks to screening
- The chances of surviving breast cancer because of the screening (avoiding breast cancer mortality)
The researchers made the following estimates for a 50-year old woman:
- During the next ten years she has a 2,990 per 100,000 chance of developing breast cancer
- 64% of breast cancers are detected by mammography
- Therefore she has a 1,910 per 100,000 risk of having a screen-detected breast cancer
- Her risk of breast cancer death over a 20-year period is 990 per 100,000
- Her risk of dying from breast cancer if there were no screening would be 1,240 per 100,000, if screening mammography lowers her breast cancer death risk by 20%
- This suggests that the estimated benefit on breast cancer mortality from screening is 250 per 100,000
This means that a screen-detected breast cancer 50-year-old patient’s probability of dying from the disease is estimated to be 13% lower (250/1910) because of the mammography. If it reduces breast cancer mortality by 25% her chances of avoiding death is 17%, and just 3% if screening mammography only reduces breast cancer mortality by 5%. The authors added that similar calculations carried out for women of various ages all come up with a probability estimate of less than 25%.
The researchers concluded:
“We considered a range of values: namely, that screening mammography reduces breast cancer mortality anywhere from 5 percent to 25 percent. The values toward the high end (20 to 25 percent) reflect the randomized trial data from more than a quarter century ago.
Consequently, we believe that readers should focus on the values toward the low end (5 to 10 percent) and recognize that the probability that a woman with screen-detected breast cancer has, in fact, avoided a breast cancer death because of screening mammography is now likely to be well below 10 percent.”
Timothy J. Wilt, M.D., M.P.H., and Melissa R. Partin, Ph.D., from the Minneapolis Veterans Administration for Chronic Disease Outcomes Research and the University of Minnesota, Minneapolis, said that in their study, the researchers..:
“. . . express concerns that overly inflated perceptions of the benefits of mammography may lead to a self-perpetuating cycle of unwarranted demand for screening, overdiagnosis, overtreatment, and a continually growing population of breast cancer survivors who advocate mammography. The demographics of survivorship suggest that their concern is legitimate.
Preventive health care services like cancer screening can result in tremendous individual and public health benefits by identifying disease at early, more treatable stages or lowering a patient’s risk of developing a disease altogether. . . . they do not always provide the expected benefit and cause harms such as overdiagnosis and overtreatment.
Numerous studies have documented that the strongest predictor of mammography utilization is physician recommendation. Therefore, simple, highly effective and accurate messages can come directly from clinicians.
In conclusion, a simple science-based message can and should be delivered to many individuals considering early disease detection and treatment,” the authors note. “The opportunity and challenge for clinicians is to be that reliable source of information that ensures that our patients are able to make well-informed decisions that incorporate the best evidence into their personal values.
Written by Christian Nordqvist