Posts Tagged PCR

“Liquid biopsies” for cancer screening: Life-saving tests, or overdiagnosis and overtreatment taken to a new level?

Could a blood draw be all you need to diagnose cancer and identify the best treatment for it? Not so fast...

Could a blood draw be all you need to diagnose cancer and identify the best treatment for it? Not so fast…

I’ve written many times about how the relationship between the early detection of cancer and decreased mortality from cancer is not nearly as straightforward as the average person—even the average doctor—thinks, the first time being in the very first year of this blog’s existence. Since then, the complexities and overpromising of various screening modalities designed to detect disease at an early, asymptomatic phase have become a relatively frequent topic on this blog. Before that, on my not-so-super-secret other blog, I noted that screening MRI for breast cancer and whole body CT scans intended to detect other cancers early were not scientifically supported and thus were far more likely to cause harm than good. That was well over ten years ago. Now we have a company offering what it refers to as a “liquid biopsy” for the early detection of cancer. I fear that this is the recipe for the ultimate in overdiagnosis. I will explain.

The problem, of course, is that disease progression, including cancer progression, is not always a linear process, in which the disease progresses relentlessly through its preclinical, asymptomatic phase to symptoms to complications to (depending on the disease) death. There is such a thing as disease that remains asymptomatic and never progresses (at which point it’s hard to justify actually calling it a disease). As I pointed out in my first SBM post on the topic, at least three-quarters of men over 80 have evidence of prostate cancer in autopsy series. Yet nowhere near three-quarters of men in their 80s die of prostate cancer—or ever manifest symptoms from it. This is what is meant by overdiagnosis, the diagnosis of disease that doesn’t need to be treated, that would never cause a patient problems.

When teaching medical students and residents, I frequently emphasize that overdiagnosis is different from a false positive because overdiagnosis does diagnose an actual abnormality or disease. For example, ductal carcinoma in situ (DCIS) diagnosed by mammography leading to a biopsy is a real pathological abnormality; it is not a false positive. We just do not know which cases of DCIS will progress to cancer and which will not, leading to a question of how DCIS should be treated or at the very least whether we should treat it as aggressively as we do now, particularly given that the apparent incidence of DCIS has increased 16-fold since the 1970s, all of it due to mammographic screening programs and the increased diagnosis of DCIS and early stage breast cancer has not resulted in nearly as much of a decrease in the diagnosis of advanced stage breast cancer as one would expect if early diagnosis were having an impact in reducing the diagnosis of late stage disease.

Overdiagnosis would not be such an issue if it didn’t inevitably lead to overtreatment. DCIS, for instance, is treated with surgery, radiation, and anti-estrogen drugs. Early stage prostate cancer used to be treated with radical prostatectomy, but now more frequently with radiation. Many of these men and women didn’t actually need treatment. We just don’t know which ones. This is why over the last six or seven years a significant rethinking of screening for breast and prostate cancer has occurred. There has been a backlash, of course, but the rethinking seems to have taken hold.

Not everywhere, of course. (more…)

Posted in: Basic Science, Cancer, Diagnostic tests & procedures, Public Health

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Another antivaccine zombie meme: polio vaccine and SV40 and cancer, oh, my!

Another antivaccine zombie meme: polio vaccine and SV40 and cancer, oh, my!

The Internet has produced a revolution with respect to information. Now, people anywhere, any time, can find almost any information that they want, as long as they have a connection to the global network and aren’t unfortunate enough to live in a country that heavily censors the Internet connections coming in. In addition, anyone any time can put his or her opinion out on the Internet and it might be read by people on the other side of the planet. For example, it continually amazes me that my blatherings here are read by people in Australia and New Zealand, as well as Europe and pretty much every other continent. Before the Internet, there was no way I would ever have achieved my current measure of minor celebrity status (and I do mean minor). Now, with enough good (I hope) writing and some links from some popular sources, and I can make my opinion known worldwide.

The dark side of this is that cranks can also make their opinions known worldwide, and, all too frequently, they are much better at it than skeptics are. For example, this very blog used a generic, vanilla WordPress template for the longest time, only updating it a few months ago. Meanwhile crank websites like are decked out in the latest, greatest web accoutrements, complete with video. One other problem with the democratization of information is that there now exist what I like to call “zombie memes.” In the world of quackery and pseudoscience, these are pseudoscientific claims on the Internet that never die, no matter how often they are refuted. Generally, such memes/claims pop up, make a fuss, are refuted, and then disappear. Then a few months (or even a year or two) later, something will happen to resurrect them. Maybe it’s a clueless mortician cremating the remains of such a zombie meme during a rainstorm and letting whatever it is that resurrected the dead meme in the first place permeate the soil of a graveyard of dead memes. Maybe it involved injecting a glowing fluid into the corpse of the meme. Who knows? Who cares that much? All I know is that these zombie memes keep popping up again and again as though they were new.


Now that the World Wide Web (at least as we know it, in its graphically browsable form) is approaching its twentieth birthday, we now have enough perspective to see these things. Steve Novella pointed out one zombie meme just the other day about the MMR, as did a certain person well known to this blog. Just yesterday I noticed another of these zombie memes arising from the dead yet again to feast on the brains of the living and thus make them cranks too. (At least, that is the goal of their continual resurrection.) This one popped up at that online repository of all things quackery,, in a post by Mike Adams himself entitled Merck vaccine developer admits vaccines routinely contain hidden cancer viruses derived from diseased monkeys. Other versions of this meme pop up from time to time with titles like CDC Admits 98 Million Americans Received Polio Vaccine In An 8-Year Span When It Was Contaminated With Cancer Virus.

Let’s dive in, shall we?

Posted in: Vaccines

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