Screen detection and tumor growth rates. Cancers have different growth rates, which determine their potential to be detected by screening. Tumor A remains microscopic and undetectable by current technology (although more sensitive tests in the future might render it detectable). Tumor B eventually becomes detectable by screening (*), but its growth rate is so slow that it will not cause symptoms during the life of the individual; its detection will result in overdiagnosis. Tumor C is capable of metastasizing, but it grows slowly enough that it can be detected by screening (*); for some, this early detection will result in survival. Tumor D grows very quickly and therefore is usually not detected by screening. This will present as an interval cancer (i.e. detected clinically in the interval between screening examinations) and has a particularly poor prognosis. Note that of the four tumor types, only Tumor C has the potential to benefit from screening. Red dashed lines represent the natural history of a tumor in the absence of detection by screening. (Figure 1 from Gates, 2014).
A new stool DNA test was recently approved by the FDA for colon cancer screening. My first reaction was “Yay! I hope it’s good enough to replace all those unpleasant, expensive screening colonoscopies.” But of course, things are never that simple. I wanted to explain the new test for our readers; but before I could start writing, some other issues in cancer screening barged in and demanded to be included. They exemplify the dilemmas we face with every screening test. We have covered these issues before, but mainly in reference to mammography and prostate (PSA) screening. My article morphed into a CLT sandwich: colon, lung, and thyroid cancer screening.
The current issue of American Family Physician has a great article on cancer screening. It uses lucid graphics to illustrate lead time bias, length time bias, and overdiagnosis bias, as well the effect of varying tumor growth rates on screening success rates, all concepts that have been covered by Dr. Gorski here. Briefly, screening may do more harm than good if:
- It detects cancerous cells that never would have developed into invasive cancers or harmed the patient in any way;
- Early diagnosis and treatment decrease quality of life without reducing death rates; or
- The test falsely indicates cancer in patients who don’t have it or fails to indicate cancer in some who do. (more…)
When I wrote about colonoscopy in 2010, colonoscopy was thought to be the best screening test for colorectal cancer because it could visualize the entire colon and could remove adenomas that were precursors of cancer. But only fecal occult blood testing (FOBT) and sigmoidoscopy had been proven to decrease colorectal cancer incidence and mortality (by 16% and 28%, respectively). Observational evidence suggested that colonoscopy would reduce the incidence and the number of deaths from colorectal cancer, but there were no randomized controlled trials, and the reduction in incidence of cancer after colonoscopy screening seemed to be restricted to left-sided colon cancers, which didn’t make sense.
We still don’t have any randomized controlled trials of colonoscopy, but a 2013 case-control study from Germany compared patients with and without colorectal cancer and found that those who reported having had a colonoscopy were less likely to develop colon cancer for up to 10 years after the procedure. And now two studies published in the New England Journal of Medicine in September 2013 have shed more light on the subject.
Editor’s note: Due to technical difficulties, SBM experienced considerable downtime yesterday. I therefore decided to delay publishing this post until now. Harriet’s normally scheduled Tuesday post will also appear later.
I like to think that one of the more important public services I provide here at Science-Based Medicine is my deconstructions of alternative cancer cure testimonials. After all, one of the most powerful marketing tools purveyors of cancer quackery have in their arsenal is a collection of stories of “real patients” with cancer who used their nostrums and are still alive and well. These sorts of analyses of alternative cancer cure testimonials began right near the very beginning of my not-so-super-secret other blog way back in 2004, metastasized—if you’ll excuse my use of the term—to SBM in 2008, and have continued intermittently to this very day, most recently with a bevy of posts showing why the testimonials of Stanislaw Burzynski’s patients do not constitute good evidence that he can cure cancers considered incurable by “standard” medicine. In other words, Burzynski’s “success stories” aren’t the slam-dunk evidence he and Eric Merola want you to believe them to be regarding the use of antineoplastons to cure brain cancers.
Sometimes, these patients who believe that alternative medicine somehow cured their cancers are so transformed, so energized, that they basically devote their lives to selling, in essence, their story, along with all the stuff they did to “cure” their cancer. I just came across one such person, a man by the name of Chris Wark, whose website and blog Chris Beat Cancer sells the idea that he beat his cancer with nutrition and “natural therapies” that he used to “heal himself.” All of this wouldn’t be quite so horrible—after all, there are lots of people who believe in woo and say so publicly—except that Wark is now also selling all sorts of misinformation about cancer, at $175 for a two hour phone consultation. Regular readers will recognize right away where Mr. Wark goes wrong in his story. Even so, I think it’s worthwhile to take a look because since discovering Mr. Wark’s site I’ve seen his name popping up all over the place promoting “natural” cures, and his site has become a repository of all sorts of “alternative cancer cure” testimonials, as well as credulously promotional material for quackery like Gerson therapy, the Beck protocol, and the Gonzalez protocol.
First, let’s take a look at Mr. Wark’s story. Since his story is so simple to deconstruct, I’ll then look at more of the material on his website. Right on the front page of Mr. Wark’s website, there is a brief blurb about him that reads:
The US Preventive Services Task Force (USPSTF) recommends that everyone aged 50-75 be screened for colon cancer with any one of three options: colonoscopy every 10 years, flexible sigmoidoscopy every 5 years, or fecal occult blood testing (FOBT) every year. Conventional colonoscopy is considered the “gold standard” since it allows for direct detection and biopsy of early cancers and removal of precancerous polyps. It involves passing a long colonoscope via the rectum through the full length of the colon and is also known as optical or visual colonoscopy. A newer and less invasive alternative, virtual colonoscopy or CT colonography, is being promoted by some as the test of choice. Others disagree. One area of controversy is that CTs frequently find “incidentalomas” that require further investigation. An article in the journal Radiology highlights this problem, describing “the clinical drama that follows screening or diagnostic tests.” (more…)
Everybody knows that colonoscopy is the best test to screen for colorectal cancer and that colonoscopies save lives. Everybody may be wrong. Colonoscopy is increasingly viewed as the gold standard for colorectal cancer screening, but its reputation is not based on solid evidence. In reality, it is not yet known for certain whether colonoscopy can help reduce the number of deaths from colorectal cancer. Screening with fecal occult blood testing (FOBT) and flexible sigmoidoscopy are supported by better evidence, but questions remain. It seems our zeal for screening tests has outstripped the evidence.
Statistics show that the life-time risk for an adult American to develop colorectal cancer (CRC) is approximately 6%. Colorectal cancer is the second leading cause of cancer deaths in the United States. In the US there are currently 146,970 new cases and 50,630 deaths each year. Between 1973 and 1995, mortality from CRC declined by 20.5%, and incidence declined by 7.4% in the United States.
The US Preventive Services Task Force (USPSTF) recommends screening for colorectal cancer (CRC) using fecal occult blood testing, sigmoidoscopy, or colonoscopy, in adults, beginning at age 50 years and continuing until age 75 years. (more…)
I have often mused about the difference between being right and being influential – especially in light of the relative success of the anti-vaccine movement. Despite the fact that there is no evidence for a link between vaccines and autism, celebrities like Jenny McCarthy have manufactured public mistrust in one of the safest, most cost effective means of combating disease known to humankind.
So if scientists are not persuading the public with appeals to carefully designed trials and factual data, how should they make their point? I’m not sure I have the full answer, but I think I might have struck a nerve with the public lately. I decided to try a novel approach to communicating my concerns about pseudoscience on the Internet – and presented 20 slides at 20 second intervals to a conference of ePatients in Philadelphia. I did it with powerful and humorous images, tied together with a long Limerick. Sound kooky? Maybe so… but it resonated, and was received with cheers and applause. Now that’s how we like science to be recognized! (more…)