Cancer prevention physical examination, why so many false alarms?
Are cancer screenings useful? Physical examinations are designed to detect signs of disease early, thereby increasing the success rate of treatment. Effective cancer screenings done by health experts fall into two broad categories, some for the general public, and more for “high-risk groups”.
Are cancer screenings useful?
There is no doubt that the earlier the cancer is, the better the cure.
Grasping everyone’s mentality, various anti-cancer physical examination items have sprung up like mushrooms after a rain.
Gold packages, platinum packages, and local tyrant packages are more expensive than the other.
Is the anti-cancer check-up useful? Is it more expensive the better?
To answer this question, we must first understand what the meaning of physical examination is.
Physical examinations are designed to detect signs of disease early, thereby increasing the success rate of treatment. Its fundamental purpose is to prolong survival time, improve quality of life and reduce long-term medical costs.
Whether a physical examination is useful depends on whether it can meet the above three standards, and the anti-cancer physical examination is no exception.
What are the categories of effective cancer screenings?
Effective cancer screenings fall into two broad categories, some for the general public, and more for “high-risk groups”.
Currently the main recommended inspection items:
For the general public:
1. Breast cancer: women, starting at age 40, with annual mammography screening
2 Cervical cancer: women, starting after the age of 20, cervical smear or HPV screening every 3 to 5 years
3. Colon/rectal cancer: men and women, starting at age 50, have a fecal occult blood test every year, and a colonoscopy every 10 years.
For high-risk groups only:
1. Liver cancer: People with a history of alcoholism and hepatitis B or C virus carriers should have alpha-fetoprotein (AFP) and abdominal ultrasonography every six months after the age of 35
2. Gastric cancer: People with gastric ulcer, Helicobacter pylori infection or family history of gastric cancer should have regular gastroscopy or other examinations after the age of 40
3. Lung cancer: Smokers or those who have quit smoking for less than 15 years should have annual low-dose helical CT scans after age 55.
You can see a few things from the above:
1. There is currently no good screening method for many cancers, including brain tumors, pancreatic cancer, etc., which have a high mortality rate.
2. The population targeted and the test used by each effective cancer screening are strictly limited.
No screening is suitable for everyone, and no screening is suitable for more than two types of cancer.
3. There are no expensive tests, no PET-CT, no genetic testing, and no tumor markers.
4. Screening for liver cancer, stomach cancer, and lung cancer is limited to high-risk groups, and screening is not recommended for the general public. The reason will be explained in detail later.
These points are important, as they illustrate that the hype of ordinary people who rely on expensive medical procedures to detect all kinds of cancers is a complete fantasy.
Why is it useless for the general public to do expensive cancer check-ups?
This is mainly because of the two words spoken before, “false negative” and “false positive”.
A “false negative” is when you have a disease but the test results are normal, while a “false positive” is when you don’t have the disease but the test is abnormal. In medicine, no test is 100% accurate.
Various tests done by hospitals, whether it is blood glucose test or HIV test, have a certain probability of false negative and false positive, but the probability is very low.
In contrast, products sold over the counter in pharmacies, such as early pregnancy test strips, have a relatively high rate of false negatives and false positives, so they often lead to unexpected “surprise” or “scare”.
Cancer-prevention physical examinations are ineffective for ordinary people, mainly because there are too many “false positives”, which leads to the fact that most of the time, very healthy people are found to be “positive for cancer markers”. After multiple inspections, it was proved to be a false alarm.
Some time ago, my favorite internet writer Tim May wrote an article “About cancer, let me tell you a few words”, which was widely circulated on the Internet. Lung cancer screening”, the result was that a shadow was found, and the test was positive.
After a few months, he had another CT scan, and it was determined that the shadow was not cancer, but a false alarm. This is a classic case of over-medication due to “false positives” in cancer prevention tests.
I said at the beginning that only smokers or people who have quit smoking for less than 15 years should have low-dose helical CT scans every year after age 55.
For a young man in his 30s like Tim May who does not smoke and has no family history, he should not have a “spiral CT physical examination” at all.
Because even if he is tested positive, it is more than 99% likely to be a false positive!
For him, his body is completely healthy, he should not have a cancer check-up and live a carefree life, but because he chose to do this unreliable CT check-up, the price he paid was thousands of dollars.
After two CT scans, I and my family worried for several months. Isn’t this looking for something for yourself?
Moreover, CT itself is radioactive and may cause cancer, so it should be done as little as possible.
The key is that Ma didn’t seem to realize that he was being fooled, because he also recommended at the end of the article that “everyone, especially smokers, should have a low-dose spiral CT every year.”
This sentence is half right: old smokers It should be checked every year, but if his young fans are also called by their idols to go for “spiral CT lung cancer screening” every year, then classmate Ma is really doing a disservice.
Why is low-dose spiral CT such a cancer screening only suitable for old smokers and not for the general public?
To clarify this problem, Pineapple and everyone play a simple math game. Lung cancer occurs in less than 0.1% of the general population under the age of 50. Suppose there are 1 million people in a city, and 1,000 people actually have early stage cancer.
Assuming that the specificity and sensitivity of low-dose helical CT detection are both 99%, that is to say, 99% of those who are sick will be detected, and 99% of those who are not sick will be correctly excluded. Sounds good, right?
But what about the results of the medical examination?
In this case, 1000×99%=990 people with cancer will be diagnosed, and 1% of those without cancer (999,000) will be wrongly diagnosed with cancer, that is 999000×1%= 9990 people.
After the whole physical examination, 990+9990=10980 people will be diagnosed with cancer, of which 9990 are misdiagnosed, and the false positive rate is as high as 91%!
That is to say, 91% of people who were tested positive for cancer prevention were actually fine. And the 990 people who really have cancer will also be mixed in with the 9990 people, and it is impossible to distinguish. Therefore, all people need to do a second test, or even a third test, to be able to really confirm.
How can a test with a specificity and sensitivity of 99% have a false positive and misdiagnosis rate of 91%?
The fundamental reason is that the incidence of lung cancer is very low in the general population, and there are very few people who are really sick.
Therefore, even a little false positive probability will lead to a large number of people who are not sick being misdiagnosed.
The specificity and sensitivity of cancer screening currently on the market are far below 99%, or even below 90%.
So in the same topic, if the specificity and sensitivity are reduced to 90%, what will be the positive misdiagnosis rate? You can do the math, it’s 98.3%!
In fact, the specificity and sensitivity of helical CT lung cancer screening is not even 90%. Therefore, Tim May’s cancer checkup was almost doomed from the beginning to be a false alarm, wasting money, causing huge psychological pressure, and at the same time suffering from unnecessary radiation.
Because of this, Pineapple does not recommend the public to do various cancer screenings, especially CT screenings that have an impact on the body.
But I, like many doctors, recommend regular cancer screenings for people at high risk of cancer (long-term smokers over 55 years old, with family history, known oncogene mutations, etc.), why?
Mainly because the probability of early-stage cancer in these people is much greater than that of the general population, and the false-positive rate will drop significantly after physical examination.
For example, Julie, who had her breasts and ovaries removed due to BRCA1 gene mutation, has a 10% to 50% chance of having cancer in her organs.
Suppose we take an average of 30% and give it to 1 million high-risk patients like Julie. Doing the same cancer prevention physical examination, the false negative rate and false positive rate of 1% screening positive misdiagnosis rate is only 2%, instead of the previous 83%.
Even with a 10% false-positive rate screening, the positive misdiagnosis rate is only 20%, making cancer screening valuable.
Therefore, if you are not a high-risk group, or you have too much money to use up, you really don’t need to spend money on those expensive anti-cancer check-ups. Let’s talk about more accurate and reliable anti-cancer check-ups in the future.