Putting breast cancer statistics into perspective

In 1998, David Plotkin lamented that women were “more alarmed than they need to be about the chances that they will develop breast cancer” and more confident about a cure than they “they should be.”

It’s almost 20 years later, and we should still be concerned about our perception of breast cancer risk.

Plotkin was an oncologist, perhaps best known to a lay audience for his controversial 1998 article in The AtlanticGood News and Bad News About Breast Cancer. He laid out three facts that challenged concerns about an increase in the raw number of breast cancer diagnoses:

  1. We’re living longer. Compared to 100 years ago, women are less likely to die in childbirth or of an infectious disease. By living longer, we are more susceptible to diseases of middle and old age, which include cancer.
  2. Baby boom bulge. As boomers age, we change the statistics on all sorts of things, including cancer.
  3. Mammography. This x-ray of the breast became popular in the 1980s and contributed to an initial burst in diagnoses. It has contributed to a major increase in diagnoses of Stage 0 cancer.

Nevertheless, there has been a persistent increase in breast cancer risk. Plotkin hypothesized that our modern lifestyle is a major contributor to estrogen receptor positive breast cancer.

  • The average age of menarche has fallen from the late teens to about 12.
  • The average age of a first pregnancy has grown, and many women have only one or two children.

As a result, we are exposed to reproductive hormones over more years.

Women … may have 300 to 400 periods—fifteen to twenty times as many as their ancestors had, exposing their breasts to historically unprecedented numbers of estrogen-progesterone cycles.

And most breast cancer is correlated with estrogen and progesterone.

molecular types of breast cancer

 

Although we are not much closer to a “cure” for breast cancer today than we were when President Richard M. Nixon declared war on cancer, we’re living longer after diagnosis. Plotkin pointed out that in 1998, the age-adjusted death rate from breast cancer was little changed from the 1930s.

The latest data from the SEER database show that the age-adjusted death rate for women from breast cancer has declined to 21.2 per 100,000 women per year (2010-2014 data). At the same time, the number of deaths attributed to lung cancer has more than surpassed that drop.

cancer death rates

 

Plotkin asked, reasonably, what do we mean by “cure”?

… if a woman of sixty-five is treated for breast cancer and then dies five years later of a heart attack, was she “cured” of cancer? Her family, friends, and even her doctor might think so, because the disease never troubled her again. Indeed, a common clinical definition of “cure” is survival for five or ten years. Many researchers would be less quick to claim a cure, because the cancer might have been on its way to recurring when the heart attack intervened.

Since Nixon was in the White House, the average life expectancy for a woman in the United States has increased from 75.3 in 1973 to 81.2 in 2012.

 

What does this have to do with perception?

We now have PinkTober each year, a bonanza for marketers and those whose livelihood rests on advertising. Think about the types of stories that you see and hear, that your friends share on Facebook and Twitter. Are they of young women of childbearing age or grandmothers?

A 2013 study of almost 8,000 women in Long Island, NY, illustrates our poor understanding of breast cancer risk:

Overall, 707 women (9%) accurately estimated their risk, 3,359 (45%) underestimated risk, and 3,454 (46%) overestimated risk. In general, white women were more likely to overestimate their risk, while African American, Asian, and Hispanic women were more likely to underestimate their risk. Women with higher levels of education also tended to overestimate their breast cancer risk (emphasis added).

That study mirrored results from a 2005 survey of 1,700 women which noted that:

Among women at average risk, those who were younger, had a family history of breast cancer, had no history of childbirth, or had more frequent exposure to lay media information about breast health were more likely than women without these characteristics to overestimate their future risk (emphasis added).

However, that “a majority of women at high risk of developing breast cancer underestimate their risk.”

Why do we overestimate risk?

One reason may be media portrayal of breast cancer, which shifts into high gear each fall. Stories on TV and in newspapers and magazines tend to be personal and emotional. These stories often “misrepresent the age distribution of the disease, focusing on atypical cases of early-onset breast cancer and their often dramatic social impact.”

However, the median age at which breast cancer is diagnosed, at this writing, is 62 years of age. More than half of breast cancer deaths occur in the 65 and older age group.

breast cancer incidence and deaths

Another reason we might overestimate risk:  risk assessments are often presented opaquely.

In 1996, many women were concerned after publication of a review of the association of breast cancer and hormonal contraceptives which stated that the risk of breast cancer was increased by 20% in users… If the risk was communicated as an absolute risk increase from 16 to 18.7 per 10,000 women or one additional breast cancer diagnosis per year among 3,700 women taking oral contraceptive, risk perception would have been totally different (emphasis added).

One reason that there is a difference between how experts and lay people assess risk is that we think of risk differently. Risk consultant David Ropeik points out that scientists think of risks as “hazard times exposure equals consequence.” Lay people hold a different definition: “the probability of something bad happening.”

Moreover, we perceive things as being more “risky” when we have no control (unless it’s nature at play); the event has catastrophic potential or fatal consequences; or if there is an inequitable distribution of risks and benefits. Cancer slips into those first two groups.

Then add innumeracy to the communications equation and we get situations like those described here.

Talk to your doctor about your risks, and then act. Take steps to mitigate high risks and table the worry about those things which are unlikely to happen.

 

 

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