Perception, expectation, risk, screening, and cancer reality

Over the past 20 years, the role of “screening” as a mechanism for early diagnosis of several types of cancer (and other diseases) has become a high-profile and emotional issue in which the value of accurate data has often been swamped by media hype and the claims of specific interest groups. This is true for prostate cancer and other forms of cancer too.

An interesting article by Davidson et al. in the American Journal of Obstetrics and Gynecology has just offered us some insight into how perceptions and expectations of target audiences may now be affecting our beliefs about what screening can actually achieve. The article is also discussed in some detail on the web site

Davidson and her colleagues surveyed 247 women aged between 39 and 49 about breast cancer screening. All of these women had come to a mammography center for a standard screening mammogram. They were randomized to read one of two articles about mammography as a screening method for women in the 40s, and then asked to complete a survey.

The results of the survey showed the following:

  • On average, these women estimated their lifetime risk for breast cancer at 37 percent.
  • 88 percent of the women overestimated their lifetime risk for breast cancer.
  • 89 percent wanted to have annual mammograms in their 40s.
  • 86 percent believed that any changes to current US Preventive Services Task Force (USPSTF) guidelines would be “unsafe.”
  • 85 percent would refuse to delay breast cancer screening until age 50 — even if this was physician recommended.
  • Women with a friend or relative with breast cancer were more likely to
    • Want annual mammograms in their 40s (92 vs 77 percent, P = 0.001)
    • Feel changes to the guidelines to be “unsafe” (92 vs 69 percent, P ≤ 0.0001).
  • Women with previous false-positive mammograms were less likely to accept doctor-recommended screening delay until age 50 (8 vs 20 percent, P = 0.01).

In assessing the data above, it is important to appreciate the following, which are data accepted by a majority of the medical science community:

  • A woman’s  lifetime risk for breast cancer is about 12 percent (1 in 8 women will have a diagnosis of  breast cancer in her lifetime)
  • About 30 out of every 1,000 women in their 40s will die from breast cancer in the absence of screening.
  • If breast cancer screening is started at age 50 and done every 2 years until women hit 75, seven of those 30 deaths would be prevented.
  • If breast cancer screening is started at age 50 and done every 2 years until women hit 75, eight of those 30 deaths would be prevented.

In other words, the change in the guideline to start mass, population-based screening for breast cancer at 50 instead of 40 would modify risk of death from 0.7 percent to 0.8 percent (an 0.1 percent absolute increase in risk) and would still not impact risk for 22/30 women initially diagnosed with breast cancer in their 40s.

This study clearly shows that most of the women participating in this study believed they were at roughly three times greater risk for breast cancer than the national average … and of course some of them may well have been at a higher than average level of risk. However, we need to start asking some serious questions of ourselves when we learn that our beliefs are badly out of tune with well documented scientific evidence.

If a similar survey of men aged 40 to 50 years of age showed that 80 percent of them believed that their risk for a diagnosis of prostate cancer was as high as 50 percent (as opposed to the actual 16.5 percent) would the prostate cancer community become concerned that we had given men unrealistic expectations about the value of PSA testing? The “New” Prostate Cancer InfoLink certainly thinks we should, especially when we also recognize that some 25 to 35 percent of all prostate cancers diagnosed are indolent in nature.

Where did the women get the idea that their lifetime risk of breast cancer was of the order of 37 percent? Well one source might be the factually accurate statement that “one in three women will now be diagnosed with cancer in their lifetime.” However, that statement refers to all forms of cancer, and not just breast cancer. That’s why we picked the comparative figure of 50 percent for men and prostate cancer mentioned above. One in two men are now going to be diagnosed with some form of cancer in their lifetime. Cancer risk is a function of age. As we live longer our risk for a diagnosis of cancer rises — significantly. One of the very best ways to avoid a diagnosis of cancer is not to live too long!

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