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  • [♪ INTRO]

  • In 1985, a post-mortem study of 101 people in Finland

  • found that 35.6% of the subjects had thyroid cancer.

  • The researchers went on to argue that if they had examined the tissue more thoroughly,

  • they expect most, if not all, of their subjects

  • would have had at least one small tumor in their thyroid,

  • and for clarity, these were people who were not diagnosed with thyroid cancer prior to their death.

  • Similarly, in 2005, an American study did full body CT scans of almost 1200 people of all ages,

  • and found that 86% of them had at least oneabnormal finding.”

  • And that was just one scan on one day of their lives.

  • Studies like these suggest that if you made full-body scans part of your regular routine,

  • odds are you'd find a bunch of cancers over the years.

  • Which sounds terrifying.

  • But, it doesn't change your odds of having a life-threatening cancer.

  • See, what you'd be finding are harmless cancers that don't ever make you sick

  • or even go away without treatment.

  • So, really, what this is, is an indicator that our definition of cancer is just kind of crummy.

  • Now for a long time, cancer has been defined as any uncontrollable growth of cells in your body.

  • And that definition worked super well back when the only way we could detect tumors was

  • feeling around for weird lumps.

  • But our ability to detect strange cell growths has improved immensely,

  • especially over the past 50 years.

  • In fact, our ability to scan the human body has progressed to the point

  • where we can identify tiny abnormalities which may or may not be headed for malignancy,

  • the ability to spread between tissues.

  • And this is making many doctors reevaluate what cancers should really be consideredcancer.”

  • The old-school definition can encompass any wonky collection of cells in your body.

  • But when a cancer isn't going to be malignant, treating it doesn't really prevent anything.

  • And even malignancy isn't enough to make something worthy of being, like a quotecancer”,

  • because there are a lot of cancers which actually aren't that bad.

  • Instead, they're indolent:

  • even though they're malignant in the sense that they can spread between tissues,

  • they spread so slowly that ultimately don't cause symptoms.

  • Some even regress or disappear all by themselves.

  • Like, the teeny thyroid tumors found in that Finnish study, for example.

  • Those almost always stay small or go away, only on rare occasions do they become problematic.

  • And researchers report that, depending on the organ,

  • between 15 and 75% of diagnosed cancers are indolent.

  • Which doctors have to ask which cancers are actually worth looking for.

  • For decades, many have thought doctors should err on the side of caution

  • by basically screening everyone for as many potentially dangerous cancers as they often as they can.

  • Because, hey!

  • It catches more cancers!

  • And it's true that people who are diagnosed with early stage cancer typically live longer.

  • But screenings have also led to cancer overdiagnosis.

  • And while the tumors in overdiagnosis are harmless, the diagnosis itself isn't,

  • because people are understandably upset when they hear they have cancer.

  • They may end up taking medicines or undergoing surgeries they don't actually need,

  • which can take a toll on their bodies and their wallets.

  • Back when these screening tests were first developed, doctors made the logical prediction

  • that early detection of tumors would decrease the number of people who died from them.

  • But often, that's not what happened.

  • For instance, between 1975 and 2016, the number of people diagnosed with thyroid, kidney,

  • and skin cancers more than tripled.

  • But the number of deaths for those cancers stayed pretty much the same.

  • Because if there are really 3 or more times as many clinically-relevant cancers occurring nowadays,

  • more people should be dying from them.

  • Because while our treatments have gotten better, they haven't gotten that much better.

  • So no change in the number of deaths suggests that

  • the screening programs are really good at catching weird cell growths that don't matter medically

  • rather than catching dangerous cancers earlier on.

  • And this is likely thanks to rapid increases in imaging technology.

  • The bittersweet reality is that a lot of the time,

  • doctors can't tell the difference between cancer that needs treatment, and cancer that does not,

  • especially if the cancer is small.

  • Though, there's hope they will be able to do that someday.

  • The upside to all this is that widespread screening programs have helped scientists discover ways

  • to distinguish between dangerous malignant cancers and harmless ones.

  • For example, with breast cancers, doctors can use molecular identifiers to determine

  • if patients need chemotherapy.

  • But that kind of fine-grained sorting isn't yet available for all cancers,

  • so while scientists continue to search for diagnostic markers,

  • doctors are trying to narrow down who should be screened, when, and how, to minimize overdiagnosis.

  • Also they're trying to change how we talk about cancer.

  • Some doctors think the termcancershould be reserved for tumors

  • that are at the highest risk of becoming malignant or already are.

  • Other overgrowths or abnormal cells should be called something else specific to their nature.

  • And even malignant cancers that grow super slowly, and therefore are unlikely to cause real harm

  • whether or not they're treated, could rebranded as I.D.L.E. disorders.

  • I D L E: indolent lesions of epithelial origin.

  • But, on the upside, until we redefine cancer in a more meaningful way,

  • at least you, like, always have an iron-clad reason to get out of work.

  • Just tell your boss that if you looked hard enough,

  • you'd probably find some weird cells growing somewhere in your body.

  • Sorry, I got weird cells!

  • Got to go home.

  • Thanks for watching this episode!

  • If you liked learning about cancer overdiagnosis,

  • we also have an episode on why we haven't cured all the cancers yet which you might like.

  • Why don't you watch that one next?

  • And if you like it, too, you should probably just subscribe to the channel

  • because we have so many videos that are good.

  • I promise.

  • They're good!

  • [♪ OUTRO]

[♪ INTRO]

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がんになっても大丈夫なとき:がんの過剰診断 (When You Have Cancer, But You're Fine: Cancer Overdiagnosis)

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    林宜悉 に公開 2021 年 01 月 14 日
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