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mikeccolella

Why cancer screening has never been shown to “save lives”—and what we can do about it

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Screening itself doesn't save lives. Just because you find out you have cancer doesn't mean you are cured. We need effective treatment methods to deal with that, and given the death rates from cancer we have improved only slightly for the last decades. Therefore, prevention is still the best strategy and I think only those who have considerable risk should monitor for cancer.

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Screening may indeed lead to deaths. That is especially important for those at low risk. Of course anyone who is high risk should get screened.

Edited by mikeccolella

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Screening itself doesn't save lives. Just because you find out you have cancer doesn't mean you are cured. We need effective treatment methods to deal with that, and given the death rates from cancer we have improved only slightly for the last decades.

 

For the specific cancers for which there are widely-used screenings (the ones under debate), the lack of effective treatments really isn't the issue: there's no debate that colorectal cancer screening reduces colorectal cancer deaths (in the Minnesota Colon Cancer Control Study previously posted by Mike, "Screening reduced colorectal-cancer mortality (relative risk with annual screening, 0.68; 95% confidence interval [CI], 0.56 to 0.82; relative risk with biennial screening, 0.78; 95% CI, 0.65 to 0.93) through 30 years of follow-up. ... The reductions  ... are comparable to those reported in randomized clinical trials of screening with flexible sigmoidoscopy." None the less, as they report, "No reduction was observed in all-cause mortality (relative risk with annual screening, 1.00; 95% CI, 0.99 to 1.01; relative risk with biennial screening, 0.99; 95% CI, 0.98 to 1.01)."

 

Similarly, we have "good" treatments for early-caught breast and prostate cancer, if by "good" we narrowly mean that if you undergo them you will have a very low chance of developing a life-threatening case of that particular cancer. The actual reasons for the lack of effect on total mortality are quite different, and vary by the cancer type. In the case of prostate cancer, it hasn't been clear until quite recently that PSA screening actually even lowers prostate cancer mortality — not for lack of effective treatments, but because PSA falsely catches a hell of a lot of indolent cancers that would not become life-threatening before the person would die of other causes. To prevent 1.3 prostate cancer deaths, you have to screen 1000 men. The case is similar with breast cancer, although mammography catches a larger number of "real" cancers.

 

An important function in all of this is the fact that cancer largely occurs late in life, when the accelerating rate of mortality rate increase over age has already brough mortality from other causes to a high background level. It's been estimated that the cure of all cancers of all kinds would only  increase life expectancy at birth by ≈3.2 years, and if implemented at age 50 (closer to the situation with cancer screening) would have an even smaller effect (1). Thus, in the colon cancer study, "Our 95% confidence intervals exclude a 1.5% reduction in all-cause mortality from screening. However, the 32% reduction in colorectal-cancer mortality that we observed corresponds to only a 0.9% reduction in all-cause mortality." IOW, a real 0.9% reduction in colon cancer mortality attributable to FIT testing, even if there were zero non-cancer risks associated with either the test or the ensuing treatment, would still get lost in the noise of all the other deaths in the relevant cohort. And, the treatments intended to treat these cancers do kill a few people (particularly in the case of breast and prostate cancer), some of whom (in the case of PSA-detected prostate cancer and mammography-detected breast cancer) didn't have life-threatening cancers granted that they are aging people with life expectancies dictated by the high and accelerating rate of mortality increases with age.

 

REFERENCE

1: Olshansky SJ, Carnes BA, Cassel C. In search of Methuselah: estimating the upper limits to human longevity. Science. 1990 Nov 2;250(4981):634-40. PubMed PMID: 2237414.

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