“Cancer screenings unnecessary and harmful”?!

In “The dark side of early diagnosis” (published in September 2018 issue of Prospect Magazine), Michael Blastland suggests that “early diagnosis” of cancer and its following medical treatment are only a waste of NHS resources and the cause for “unnecessary suffering”. He asserts that statistics on this matter mislead us by using tricks “that make(…) early diagnosis appear a good thing”. For him, only those with cancer symptoms need “a proper examination and diagnosis”, not “people who are symptom-free”, because in the latter case a misdiagnosis would lead to “unnecessary anxiety, treatment—and harm”. Also people who have cancer but are “symptom-free”, do not need a screening and treatment, because in many cases their cancer “will never develop and never hurt them”, as Blastland puts forward. 

To support his point, Blastland presents a diagram with data on “the outcomes for women who are and are not screened for breast cancer”, and notes that these results “are now reported in the latest NHS breast screening leaflet”. The diagram illustrates two groups of women aged between 50 and 70. In each group there are 200 women. The 200 women in the first group attend screening. 15 of them develop breast cancer, 185 will never have breast cancer. Of those 15 who develop breast cancer and have been screened, 3 die from breast cancer, 12 are treated and survive. In the second group, there are likewise 200 women, but they do not attend screening. Exactly as in the first group, 15 of them develop breast cancer, 185 will never have breast cancer. But of the 15 who develop breast cancer and are not screened, 4 die from breast cancer, 8 are treated and survive, and 3 are “unaffected”. 

The “unaffected”, as Blastland states, “are women who have cancer that will never develop and never hurt them. Often, it’s carcinoma in situ—the ‘in situ’ meaning that it stays put in the ducts where it begins and never affects the rest of the body. If they are not screened, they never know, never worry, never have treatment—and they’ll be fine. But if these women are screened then, since we don’t know if it’s carcinoma in situ, or a cancer that could kill, they’re likely to be treated—including with mastectomy surgery. In some cases, then—and there’s no knowing which—early diagnosis will be harmful.” Blastland argues that whereas the difference in deaths between the two groups is only one in 200, in the first group (screened) all 15 women are “affected”, but in the second group (not screened) 3 are “unaffected”. He concludes that, thus, the harms of screening are greater than its benefits. 

There are two problems with Blastland’s interpretation of the data. Firstly, the difference in deaths is not one in 200, but one in 15, because only 15 of the 200 women in each group develop breast cancer. Secondly, Blastland considers a too small number of women, which leads to his underestimation of saved lives through early diagnosis. If we take a much larger number of people into account, we will get a very different picture than that described by Blastland. By multiplying the number of women in each group by e.g. 10.000, we would take four million women aged between 50 and 70 into consideration, instead of only 400. Of those 150.000 women who develop breast cancer and are screened, only 30.000 would die, whereas of those 150.000 who develop cancer and are not screened, 40.000 would die. This makes a difference of 10.000 lives among 150.000 women with breast cancer. The larger the number of people taken into consideration, the clearer the facts about the potential of early diagnosis to save lives. 

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