After studying this, you’ll know greater than an estimated 97 p.c of docs a couple of vital idea known as lead-time bias. 

Whereas operating for president of the US, former New York mayor Rudy Giuliani ran a marketing campaign advert contrasting his 82 p.c probability of surviving prostate most cancers in the US with the 44 p.c probability of surviving it in England “underneath socialized drugs” the place routine PSA testing for prostate most cancers shouldn’t be performed. “To Giuliani this meant that he was fortunate to be residing in New York and never in York, as a result of his probabilities of surviving prostate most cancers appeared to be twice as excessive in New York. But regardless of this spectacular distinction within the 5 12 months survival fee, the mortality fee”—the speed at which males had been dying of prostate most cancers—“was about the identical within the US and the UK.” How might that be? PSA testing elevated survival from 44 to 82 p.c, so how is that “not proof that screening saves lives? For 2 causes: The primary is lead time bias…The second is overdiagnosis.” 

As I illustrate at 1:05 in my video Breast Most cancers and the 5 12 months Survival Price Fable, overdiagnosis is when a most cancers that in any other case would have by no means prompted an issue is detected. Contemplate this: Let’s say that, with out screening, solely 400 individuals out of a thousand with progressive most cancers are alive 5 years later. That signifies that with out screening, the five-year survival fee is simply 40 p.c. However, let’s say that with screening, a further two thousand cancers are overdiagnosed, which means cancers that may have by no means prompted an issue or might have disappeared on their very own are picked up. So, as a result of these cancers are innocent, these overdiagnosed sufferers all nonetheless alive 5 years later, assuming their pointless most cancers therapy didn’t kill them. On this manner, the five-year survival fee has simply doubled, although in both case, the identical variety of individuals died from most cancers. If that’s complicated, watch the video. That’s a method the modifications in survival charges with screening might not correlate with modifications in precise most cancers loss of life charges. 

The opposite manner is lead time bias. Think about a bunch of sufferers who had been recognized with most cancers due to signs at age 67 and all died at age 70. Every affected person survived solely three years. So, the five-year survival fee for the group is 0 p.c. Now, think about that the identical group underwent screening. By definition, screening exams result in earlier prognosis. Suppose that with screening, the cancers had been recognized in all sufferers at age 60 as a substitute of 67, however, however, all of them nonetheless died at age 70. On this screening situation, every affected person survived ten years, which makes the five-year survival fee for this group one hundred pc. Survival simply went from 0 to one hundred pc! You possibly can think about the headlines: “ Most cancers sufferers stay 3 times longer with new screening check, ten years as a substitute of three.” All that basically occurred on this screening situation, although, is that the individuals had been handled as most cancers sufferers for a further seven years. If something, that may seemingly simply diminish their high quality of life. 

So, that’s the second manner that modifications in survival charges with screening might not correlate with modifications in precise most cancers loss of life charges. The truth is, the correlation is zero, as you possibly can see at 3:14 in my video. There is no correlation in any respect between will increase in survival charges and reduces in mortality charges. That’s why “[i]f there have been an Oscar for deceptive statistics, utilizing survival statistics to choose the good thing about screening would win a lifetime achievement award palms down. There is no such thing as a strategy to disentangle lead time and overdiagnosis biases from screening survival knowledge.” That’s why, “within the context of screening, these statistics are meaningless: there is no such thing as a correlation between modifications in survival and what actually issues, modifications in how many individuals die.” But, that’s what you see within the advertisements and leaflets from many of the most cancers charities and what you hear from the federal government. Even prestigious most cancers facilities, like M.D. Anderson, have tried to hoodwink the general public this manner, as you possibly can see at 3:57 in my video.

In case you’ve by no means heard of lead time bias, don’t fear, you’re not alone. Your physician might not have heard of it both. “Fifty-four of the 65 physicians [surveyed] didn’t know what the lead-time bias was. Of the remaining 11 physicians who indicated they did know, solely 2 defined the bias accurately.” So, simply by having learn up to now on this weblog publish, it’s possible you’ll already know extra about this than 97 p.c of docs. 

To be honest, although, is it potential the docs don’t acknowledge the time period however perceive the idea? No. “The vast majority of main care physicians didn’t know which screening statistics present dependable proof on whether or not screening works.” The truth is, they “had been additionally 3 instances extra prone to say they’d ‘positively advocate’ a [cancer screening] check” primarily based on “irrelevant proof,” in comparison with a check that truly decreased most cancers mortality by 20 p.c. 

If physicians don’t even perceive key most cancers statistics, how are they going to successfully counsel their sufferers? “Statistically illiterate physicians are doomed to depend on their statistically illiterate conclusions, on native customized, and on the (largely) inaccurate guarantees of pharmaceutical gross sales representatives and their leaflets.” 


  • Overdiagnosis, the detection of most cancers that in any other case would by no means have prompted an issue, may end up in pointless most cancers remedies and have an effect on survival charges of breast most cancers sufferers.
  • For instance, with out screening, the five-year survival fee is 40 p.c. With screening, nonetheless, overdiagnosis leads to extra most cancers sufferers, regardless of the chance that their cancers are innocent or might disappear on their very own. And, these overdiagnosed sufferers must be alive after 5 years, which doubles the five-year survival fee, although the identical variety of sufferers died from most cancers.
  • Lead time bias can also be a difficulty. Symptomatic sufferers could also be recognized at a later age than had they been with screening, which, by definition, results in earlier prognosis. On this case, think about sufferers had been recognized with out screening at age 67 and died three years later, so the five-year survival fee is 0 p.c. Now think about the group underwent screening and the cancers had been recognized at age 60, in order that they had been alive for ten years earlier than dying at 70. Within the screening situation, the five-year survival fee for the group is one hundred pc.
  • The truth is, there is no such thing as a correlation between will increase in survival charges and reduces in mortality charges.
  • It’s not potential to disentangle the biases of lead time and overdiagnosis from screening survival knowledge.
  • The overwhelming majority of docs—54 out of 65 physicians surveyed—are unfamiliar with lead time bias, and of the 11 who indicated they did know, solely 2 defined the bias precisely.
  • How can docs who don’t even perceive key most cancers statistics successfully counsel their sufferers?

There’s simply a lot confusion with regards to mammography, mixed with the corrupting business pursuits of a billion-dollar business. As with every essential well being choice, everybody must be absolutely knowledgeable of the dangers and advantages, and make up their very own thoughts about their very own our bodies. That is one installment in my 14-part collection on mammograms, which incorporates:

For extra on breast most cancers, see my movies Oxidized Ldl cholesterol 27HC Could Clarify Three Breast Most cancers MysteriesEggs and Breast Most cancers and Flashback Friday: Can Flax Seeds Assist Forestall Breast Most cancers?

I used to be capable of cowl colon most cancers screening in only one video. In case you missed it, see Ought to We All Get Colonoscopies Beginning at Age 50?.

Additionally on the subject of medical screenings, take a look at Flashback Friday: Value Getting an Annual Well being Verify-Up and Bodily Examination?Is It Value Getting Annual Well being Verify-Ups? and Is It Value Getting an Annual Bodily Examination?

In well being,

Michael Greger, M.D.

PS: In case you haven’t but, you possibly can subscribe to my free movies right here and watch my stay displays:


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