This is the first of a series of posts about screening for breast cancer. Yes? No? When? How often? are questions DISCLAIMER: (Needed so my lawyers’ cortisol levels stay in a healthy range 😉 ) The information provided therein cannot possibly replace the individualized advice of the health care professional familiar with your health status. that come up with increasing frequency as the population advances in age. Our goal here is to clarify some of the fundamental concepts underlying screening, its advantages and drawbacks and the context it takes place.
An often used argument coming from the advocates of the superiority of screening early and often for a host of conditions runs like this: “Survival rates for breast cancer,The same can be said for colon cancer and prostate cancer are the best when screening is done early and often.”
In general, such attitudes are based on a simple concept that makes a lot of intuitive sense: the earlier you can detect cancer, the better outcomes will be. Early intervention will beat late diagnosis any day of the week, hands down. For example, the five-year survival is much higher for treated stage I breast cancer than for treated stage III.
It only seems logical to extend this first intuition to the population as a whole. By testing even people who don’t present symptoms, we hope to catch a significant disease before it disables or kill. This whole construct constitutes the rationale for public health screening.
Be that as it may, it bears to keep in mind an iron-clad rule of health and wellness care: by action or omission, whatever we do will bring consequences. The key is to give ourselves the tools to evaluate risks over benefits. It would be very nice indeed if we could fulfill our quest for certainty. Alas, health isn’t the space where it will happen. Therefore, our first task is to understand some basic concepts about health screening.
- Mortality rate defines the number of people who die from a certain cause in a given year divided by the population. For instance, the mortality rate for people with lung cancer in the United States was 59.8 males versus 37.8 females per 100,000 people during the period 2005 -2011. For breast cancer, the rate was 10.6.
- The survival rate is an entirely different animal. It is a calculation of the percentage of people with a disease who are still alive a set amount of time after diagnosis. The five-year survival rate for people with lung cancer in the US was 15.6% during the period 2005 -2011. For breast cancer, the rate was 89.4% during the period 2005 – 2011.
The implications derived from these definitions are quite significant. There are only two ways to decrease the mortality rate; prevent death, or cure the disease. You either cure the disease or prolong life, hopefully in good health. Needless to say, both outcomes are highly desirable.
The survival rate is increased the same ways as the mortality rate. (preventing death, or curing the disease) However, we must add a third option; getting diagnosed earlier. This simple third option can prove very problematic in real life.
To illustrate this, let’s engage in a thought experiment. Say a new form of cancer X emerges in humans. It’s quite lethal. People with cancer X live ten years after starting treatment if X is detected very early, four years after the first visible red spot. Now, assume it is almost impossible to identify cancer X before the first red spot appears. In such a case, the survival rate (measured at five-year) will be zero since from detection to demise, only four years have passed.
What comes next is entirely predictable. There is a mad dash to invent a diagnostic test and discover a better treatment, which will be touted as a “cure.” Low and behold, the same story we witnessed 30 years ago with AIDS.
We get the test; people get a diagnosis six years earlier than before, but there is no improvement in the treatment of cancer X, despite getting treatment earlier and earlier. People are still dying four years after the first red spot appears. BUT…the survival rate has increased to almost 100%! All those diagnosed early live close to ten years with the disease.
The plot thickens by several units of density when it turns out on the other side of the Atlantic Ocean, health authorities in Europe decided not to implement the screening test before having better data. Their survival rate will be 0% even if their mortality rate will be very similar to the American rate.
How’s that for willful distortion? For similar mortality rates, one could easily believe many more people in the US survive while Europeans would be decimated by inferior care and…gasp! rationing. (Like, we do not ration by health insurance and income here…right?)
If this thought experiment strikes you as fictional and far-fetched, here’s a reality check. In the United Kingdom, women with average risk of developing breast cancer undergo their first mammography at age 50 and get tested every three years after that. In the United States, the American Cancer Society recommends first screening at age 40 Changed very recently to 45 and every year after that.
What does this all means? Let’s skip the statistical geekiness, percentages and all As a comparative example, let’s see the data UK v. US: For a woman diagnosed with breast cancer in 2001, the five-year survival rate in the US was 89.1%; in England it was 86.6% for a woman diagnosed with breast cancer in 2011. As for the mortality rates, the data from 2009 reports it was 25.0 per 100,000 women in the US, and Cancer Research UK reported a rate of 26.7 per 100,000 women in England. and examine a translated version of said statistics in plain English:
For every 1,000 women aged 50 years or older who participated in screening for a decade or more:
- 4 died of breast cancer versus 5 in 1,000 women who did not screen.
- The same number of women (n=21) died from cancer of any type, whether they underwent screening or not.
- 100 screened women who turned out NOT to have cancer experienced a false alarm or biopsies.
- 5 screened healthy women were diagnosed and treated for breast cancer unecessarily versus none in the unscreened group.
Such a difference in mortality (4 versus 5) can hardly qualify as significant when one considers the harms of unnecessary treatment (did any of these women died because of it?) and the unecessary biopsies, which is still a surgical intervention. It is important to remember there is no surgical intervention without risks.
Thus, one wonders why are the recommendations for screening so much more aggressive in the USA? And more to the point, what does that mean for American women? The answers will be the object of a second post.
References & Footnotes [ + ]
|1.||⇑||DISCLAIMER: (Needed so my lawyers’ cortisol levels stay in a healthy range 😉 ) The information provided therein cannot possibly replace the individualized advice of the health care professional familiar with your health status.|
|2.||⇑||The same can be said for colon cancer and prostate cancer|
|3.||⇑||Changed very recently to 45|
|4.||⇑||As a comparative example, let’s see the data UK v. US: For a woman diagnosed with breast cancer in 2001, the five-year survival rate in the US was 89.1%; in England it was 86.6% for a woman diagnosed with breast cancer in 2011. As for the mortality rates, the data from 2009 reports it was 25.0 per 100,000 women in the US, and Cancer Research UK reported a rate of 26.7 per 100,000 women in England.|