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Lung cancer screening, why low-dose CT is recommended? Can other cancers be used?

Original title: Screening for lung cancer, why is low-dose CT recommended? Can other cancers be used?

Text | Pineapple

Lung cancer is the largest cancer type in China, and it ranks first in terms of both the number of cases and the number of deaths.

The good news is that with the advent of targeted therapies and immunotherapy, the therapeutic effects of advanced lung cancer have developed rapidly. In many lung cancer subtypes, the 5-year survival rate of advanced patients has increased from less than 4% to about 20%.

Further reading:

But Pineapple feels that more important than the frontiers of treatment is screening for lung cancer.

In the face of any cancer, early treatment is far better than late. Lung cancer is no exception. No matter how much progress has been made in the treatment of stage 4 lung cancer, compared with the clinical cure rate of more than 90% in early stage lung cancer, it is also beyond reach.

The value of early detection of a tumor is not only that it can greatly improve the cure rate, but also save a lot of money and significantly reduce economic toxicity. For the majority of Chinese people, knowing effective screening methods and avoiding advanced cancer as much as possible is the most cost-effective choice.

Today, we will talk about how to screen for lung cancer.

Speaking of lung cancer screening, the most important question is what method should be used for screening?

低剂量CT,一年一次! In fact, the answer is very simple. At present , there is only one lung cancer screening method recommended by authoritative organizations: low-dose CT, once a year!

Everyone will find that if you search for "lung cancer screening", there will be a variety of lung cancer screening packages on the Internet, and the methods used will be various. There are routine medical examinations such as X-ray chest radiography and serum tumor markers, as well as high-end programs such as PET-CT and genetic testing.

But everyone must know that no matter what the price is, these screening methods are not as effective as low-dose CT due to different reasons, which is not a good choice.

X-ray chest radiograph

Although easy to operate, the main drawback of this test is that it is easy to miss diagnosis and is not suitable for early tumor screening. For example, it is difficult to find tiny tumors <5 mm, insensitive to non-calcified small nodules, detection of dead corners, undetectable tumors in some parts of the lung, and so on.

Serum tumor markers

The specificity and sensitivity are not high. When used for screening, false negatives (no cancers are detected) and false positives (no cancers are detected) are significant, and the effect is not good.

Therefore, the above two methods cannot be used as standard methods for lung cancer screening, and can only be used as a routine medical examination. If no problem is found, it does not mean that there is no lung cancer. Conversely, if a problem is found, it cannot be determined, and CT and other means are needed to verify it.

If it is not cheap, why is it expensive? What about the inspection method that looks very big?

PET-CT

This kind of test is very expensive, at least several thousand, or even tens of thousands. It is not good for early cancer screening, and it is prone to misdiagnosis, especially false positives. Its technical characteristics make it better to detect advanced cancer. 性价比低 In short, it is cost-effective for early screening .

You might say, "I don't run out of money and don't mind being misdiagnosed. I'm just afraid of cancer. Isn't there any harm in doing it?"

Really bad! PET-CT is not harmless, it has a significant risk, which is radiation!

Both PET and CT are ionizing radiation, which is itself a " carcinogenic risk. " PET-CT is a combination of the two, and the radiation dose is also superimposed. Generally speaking, the average radiation dose of a PET-CT is 25 millisieverts (mSV), which is equivalent to 7 to 10 years of sun exposure. 想了解更多原理知识,请读 PET-CT:是个好技术,但别拿来搞癌症筛查! ) (For more principles, please read PET-CT: It's a good technique, but don't use it for cancer screening!)

Therefore, in regular hospitals, this technology is generally used for the diagnosis of cancer and the monitoring of the effect of treatment (including recurrence or metastasis). For these patients, the advantages of PET-CT outweigh the disadvantages, because it is the most urgent task to know the location of the cancer and understand whether it recurs. Under the tradeoff, you can sacrifice the risk of some radiation.

But no responsible doctor will let healthy people do PET-CT for no reason. Because there are other screening methods with much lower risk, blindly using PET-CT for mass cancer screening has far greater risks than benefits.

Therefore, there is no authority in any country in the world, and PET-CT is recommended for early screening of any cancer. But now there are many marketing articles from businesses on the Internet. Pack it into a "high-end physical examination" that is beneficial and harmless. Everyone must be careful not to be fooled.

Low-dose spiral CT is currently the most cost-effective lung cancer screening method.

Low-dose spiral CT, as its name suggests, is a relatively low-dose CT.

The low-dose CT has a radiation dose reduction of 75% to 90% compared to conventional CT, and the inspection cost is lower. At the same time, it overcomes some weaknesses of X-ray chest radiographs, including the ability to find tiny lesions of a few millimeters, and it can also find a very small location. Tricky tumor.

But experts recommend low-dose CT for screening. The most important reason is not that it is useful in theory, but that the test data proves it useful!

Statistics from the United States show that early-stage lung cancer accounts for 85% of cancers detected by low-dose CT, and many people are completely asymptomatic. At the same time, the overall 10-year survival rate of lung cancer patients detected by screening is as high as 80%; if timely surgery can be performed, the total 10-year survival rate is as high as 92%.

In 2011, the results of a randomized controlled study of the National Lung Screening Trial in the United States showed that compared with X-ray chest radiographs, screening low-dose CT for high-risk lung cancer populations can reduce lung cancer mortality by 20%. .

These data prove that screening low-dose CT for high-risk populations of lung cancer can find more early resectable lung cancer in high-risk populations and reduce mortality of advanced lung cancer.

That's the question. If low-dose CT is so useful for screening, why can't other high-risk cancers, such as liver cancer, stomach cancer, and pancreatic cancer, be used for screening?

Because the lungs have different structures from other tissues and organs, the lungs have more air content and lower density, so low-dose CT can form a satisfactory image.

Other tissues in the human body are more dense, and small tumors appear, and low-dose CT is a little helpless, requiring other technical means.

(four)

So who should be screened for lung cancer?

Not a little girl in her 20s who never smokes, but a "high-risk group."

Who are the high-risk groups? The Chinese and American guidelines have slightly different definitions. The current mainstream definitions in China are:

1. Age over 40.

2. At least one of the following risk factors:

  • Smoking is ≥20 pack years, and quitting time is <15 years. The so-called "≥20 pack years" refers to the number of cigarettes smoked per day x the number of smoking years ≥20. For example, smoking two packs of cigarettes per day for more than 10 years, or one pack of cigarettes per day for more than 20 years, this is ≥20 pack years.
  • Occupational or environmental exposure to various carcinogens (such as asbestos, beryllium, uranium, plutonium, etc.)
  • Have a history of malignant tumors or a family history of lung cancer;
  • Have a history of chronic obstructive pulmonary disease (COPD) or diffuse pulmonary fibrosis.

3. Consider indoor and outdoor air pollution, including long-term exposure to second-hand smoke, cooking oil fume, and air pollution.

1. Age over 40.

2. At least one of the following risk factors:

  • Smoking is ≥20 pack years, and quitting time is <15 years. The so-called "≥20 pack years" refers to the number of cigarettes smoked per day x the number of smoking years ≥20. For example, smoking two packs of cigarettes per day for more than 10 years, or one pack of cigarettes per day for more than 20 years, this is ≥20 pack years.
  • Occupational or environmental exposure to various carcinogens (such as asbestos, beryllium, uranium, plutonium, etc.)
  • Have a history of malignant tumors or a family history of lung cancer;
  • Have a history of chronic obstructive pulmonary disease (COPD) or diffuse pulmonary fibrosis.

3. Consider indoor and outdoor air pollution, including long-term exposure to second-hand smoke, cooking oil fume, and air pollution.

The third point is the relatively large difference between China and the United States.

Unlike other countries in the world, it is very strange that China has a large number of non-smokers, especially women with lung cancer. At present, it is believed to be related to various indoor and outdoor air pollution. China is the country with the most severe second-hand smoke, and more than 700 million people are harmed by second-hand smoke.

Therefore, even if you do not smoke at all, adults over 40 should self-assess their risks to see if they need screening.

It is worth mentioning that because lung cancer takes an average of 15 to 20 years, even if it has been exposed to risk factors (such as second-hand smoke) for a long time, it has recently improved, it should be noted.

If it is really not a high-risk group, but the individual would like to be screened, can I?

From a purely scientific perspective, screening for high-risk populations has the highest value, but cancer screening is ultimately a matter of personal choice. Everyone knows the benefits and risks of screening. If non-high-risk groups have to screen for lung cancer, they can consider reducing the frequency, such as once every 2-3 years instead of once a year. After all, low-dose CT still has radiation, and it also costs money.

Cancer screening is about balancing risks and benefits, and everyone should make decisions based on their needs.

(Fives)

Looking forward, there are two directions worth looking forward to.

The second is the emergence of non-invasive and radiation-free screening methods. In the future, it is possible to use "liquid biopsy screening", that is, using sputum, saliva or blood to detect mutations in genes, combined with other indicators to determine a person's risk of lung cancer. This will be more convenient and safer, and more people can be screened. But this is still in the research stage, and it is too early to recommend it.

In short, everyone remembers that there are two main points in lung cancer screening:

  • High-risk groups are recommended to be screened once a year!
  • The only official recommendation is low-dose CT!

So, what to do to screen out lung nodules? Let's talk slowly next time.

1. ReducedLung-Cancer Mortality with Low-Dose Computed Tomographic Screening. New England Journal of Medicine. 365 (5): 395–409.

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