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Public health, lead time bias, and The Dude

Prof. Devi Sridhar in The Guardian about the epidemic of missed cancer cases:

Early [cancer] diagnosis is important because it improves survival outcomes. In England, more than 90% of people survive bowel, breast and ovarian cancer for at least five years if diagnosed at the earliest stage. This allows treatment to start earlier, before the cancer has spread through the body. Yet even with a cancer diagnosis, the NHS is struggling to provide treatment within the current 62-day target time: 36% of patients waited longer than 62 days in England, 21% in Scotland and 43% in Wales. The main bottleneck is staff shortages, which the Covid-19 pandemic has made more acute. Again, this points to the need for investment in the NHS – in not just infrastructure, but also the workforce.

Prof. Sridhar is chair of global public health at the University of Edinburgh so I was surprised to see her make a basic error in epidemiological reasoning. “Early cancer diagnosis is important because it improves survival outcomes”, the paragraph begins, citing not original research but a comment in The Lancet which, yes, is a prestigious journal, Impact factor 202.731, which is ridiculously high. but calling on comments to back your claims without primary literature are level 0 data.

The Lancet article There is a story here about going down rabbit holes due to poor citation practices — I once spent two days hunting for the primary reference to a single sentence for a letter in a journal nobody reads — that deservs a post of its one. One day., “Earlier diagnosis: the importance of cancer symptoms” does refer to a 2015 systematic review of 209 studies in the British Journal of Cancer — not as prestigious, you’ll notice Impact factor 9. — whose main conclusion was that the studies were of such varying quality that “Heterogeneity precluded definitive findings”.

The authors did speculate in the conclusion that they “believe that it is reasonable to assume that efforts to expedite the diagnosis of symptomatic cancer are likely to have benefits for patients in terms of improved survival, earlier-stage diagnosis and improved quality of life, although these benefits vary between cancers”. Which, fair enough, but: number one, that’s just like, your opinion, man; and number two: there is already a plethora of data about lead time bias fooling you into thinking your early detection prolongs survival when in fact all it did was make the person aware they had cancer for longer without making an iota of difference on when and of what they would die. I base this claim purely on personal anecdote, where people “cured” of their lymphoma were reluctant to get a mammogram — a possible side effect of chest radiation — so they wouldn’t have the aura of cancer hang above them once again. Since this is a situation for which we know that when the cancer does occur, a so-called “secondary malignancy”, it is more aggressive than usual, they ended up doing it, and good for the patient! Yes, there are people who would rather know, but a good proportion — as this is a blog post and not a commentary in The Lancet I am going to allow myself some speculation here — possible more than half would rather not!

So what is going on here? Surely the chair of global public health at a well-known university knows about the lead time bias? The last three years made me question jumping to that conclusion right away, but let’s give some benefit of doubt. The key word here, I’m worried, is public health, a blunt-force instrument which does away with nuance in favor of broad if not deep messages and interventions. Sometimes these are terrifyingly successful: witness the eradication or near-eradication of infectious diseases, or my favorite — plummeting smoking rates in the United States after a public campaign and a flurry of lawsuits that saved more lives than all statins and chemotherapeutics put together. But the dangers of oversimplification are real, like the crusade to ban saturated fats in favor of simple processed sugars backfiring spectacularly. Caveat audiens.

So anyway, that’s why I don’t read newspaper coverage of medical matters, opinion pieces, or The Guardian.

Thats just like, your opinion, man

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