Flaws With the 98% Survival Rate Statistics You’ve Been Told
Susan G. Komen Foundation is the world’s largest breast cancer charity and creator of the “pink ribbon” that you see everywhere, especially during the month of October. This charity, who receives around $200 million a year (source) in contributions from public support, is best known for promoting mammography screening. Although Susan G. Komen Foundation has modified their marketing statistics over the years, their marketing messages for mammography are still ingrained in many of us. We’ve been told over and over that “early detection saves lives” and that the “5-year survival rate for breast cancer when caught early is 98%”.
Their advertising sounds amazing. Why wouldn’t someone get their regular mammogram?
Yet, there are a few flaws with their numbers. Without mammography screening, a diagnosis is made when the tumour can be felt. With screening, diagnosis is made years earlier when tumours are too small to feel. Using a five-year survival only looks at the proportion of women who are alive 5 years after diagnosis. By using mammography to detect cancers earlier, comparing survival with such a short 5-year period between screened and unscreened women is extremely biased.
In a study posted in the BMJ on How a Charity Oversells Mammography, Barnett Kramer, Director of the National Cancer Institute’s Division of Cancer Prevention, explained this bias by using an analogy to an old cartoon, The Rocky and Bullwinkle Show. In a recurring segment, Snidely Whiplash ties Nell Fenwick to the railroad tracks to extort money from her family. Once the train comes, she will die. Kramer describes lead time bias is “like giving Nell binoculars. She will see the train – be ‘diagnosed’ – when it is much further away. She’ll live longer from diagnosis, but the train still hits her at exactly the same moment.”
In other words, imagine a group of 100 women who didn’t received diagnoses of breast cancer until age 67 when they felt a lump. Let’s say they all die at age 70. Now, let’s pretend another group of women had regular mammography screenings and detected an earlier stage of cancer at age 64. For this example, pretend that these women also die at age 70. The 5-year survival group in the first group was 0%, where the second group was 100%. Do you see the bias?
Another issue with the Komen’s survival rate statistics is it includes all the overdiagnosed cases. These statistics distort the survival rates because the numerator and denominator now include people who have a diagnosis of cancer and who survive the cancer (even though what they had was harmless and would have healed on its own). The greater the number of overdiagnosis that occurs, the greater the inflation. If you think that overdiagnosis by mammography is rare, be sure to check out our article on Do Regular Mammogram Screenings Reduce Breast Cancer Mortality.
