I am extremely skeptical about tests like these. Screening for cancer (or any other disease) should have strong evidence to back it, failing which the test will only exploit innocent public. What do I mean by evidence to support it?
Thread
Thread
The only reliable evidence to support screening is from large randomized trials offering screening to one arm & routine care to the other, & conclusively demonstrate decreased mortality in the screened arm. Sorry, but no alternative expedient methods of "evidence" matter. Why?
Screening has the real potential for harm, by way of unnecessary tests, interventions that can cause harm, or even death, diverting scarce health resources to useless treatment & costs involved. Which is why, if there is no mortality reduction, the screening tool is merely a tool
Screening for asymptomatic disease is subject to multiple biases including overdiagnosis, lead-time and length-time bias. All of these result in improved survival in the screened arm but no reduction in mortality. Survival is a poor endpoint in a screening trial. Why?
In survival analysis, the denominator is the number of patients diagnosed, which is invariably higher in every screening study, because it picks up non-lethal, inconsequential disease. Yes, this subset exists even in diseases like lung cancer!
In mortality, the denominator is the entire population being studied, which is the relevant part on a screening study. Unless a cancer screening study demonstrates decreased mortality in the screened arm, it is useless, ineffective and possibly harmful. Next, let's...
look at evidence for "general health checks" in reducing illness and mortality. There is a Cochrane systematic review which concludes "systematic health checks are unlikely to be beneficial and may lead to unnecessary tests and treatments". (Krogsboll LT et al)
The UK NHS and the Canadian Task Force recommended that the "routine annual health check be abandoned". The #choosingwisely campaign recommends against annual preventive examinations in asymptomatic individuals.
I went through the "evidence on the world's largest trial conducted right here in India" tweeted by @liquidbiopsy360
This is by no stretch of imagination adequate data to support using circulating tumor cells to diagnose asymptomatic individuals for screening. Why?
This is by no stretch of imagination adequate data to support using circulating tumor cells to diagnose asymptomatic individuals for screening. Why?
The study was done on 5500 patients with cancer and 10600 asymptomatic individuals. 90% of the results deal with the patients who already had a diagnosis of cancer and are therefore completely irrelevant in the screening arena. Why have the authors not focused on the 10600?
Of these 10600 individuals, 392 had CTCs detected in their blood. Of these, 255 had CTCs with no abnormality on a host of additional cancer-detection tests. And none of the 392 individuals had presented with any clinical or radiological manifestations of cancer!
I struggle to understand how this "evidence" is being used to support screening asymptomatic individuals using CTCs. Based on this data, it is at best useless, and at worst, harmful to advocate this.
The countless additional tests, the anxiety and the Damocles' sword of a future cancer diagnosis hanging over these 392 individuals, with no perceivable benefit. And now being promoted to millions of others. I shudder. Primum non nocere, dear doctor.
