As a cancer researcher, I tried to answer why cancer is refractory from a genetic point of view.
One of the big reasons why cancer is refractory is its genetic heterogeneity. In cancer, it refers to: the same cancer may be caused by different mutations. There are many literatures in this field, and I try to speak in very common language.
We can think of cancer as a very large army, in which every soldier is equivalent to a cancer cell. So how big is this army? When we can see it in the hospital, it has reached the order of 10 9 (that is, 1 billion).
Difficulty 1. Cancer [Base Camp] Various Arms
Now the question arises, are the billion soldiers exactly the same?
The answer is no.
Some of them have knives, some have swords, some have tanks, some have planes. This brings us the first layer of difficulties in treating cancer: if we use drugs to attack the cancer army, there are always a few arms that we cannot handle, and there will always be some surviving cancer tissues after such a round of drugs.
Over time, these survivors can form large forces through reproduction (i.e. Cell division).
Difficulty 2. The scattered small troops split into different armies.
So you said, no matter how miscellaneous this team is, can we directly cut off the entire cancer tissue?
The answer is: it can only be solved for a short time. Most of the deaths of cancer patients are due to the metastasis of cancer to places where surgery cannot be performed, such as brain, lung and other organs.
Because cancer troops are highly mobile and can move everywhere, and most of the time, cancer is transferred by small troops (the term is metastasis, which is what we often hear about [cancer metastasis]), we have no way to detect it at all.
By the time we can detect it, the small army will have split into 100,000 troops.
In addition, as we said earlier, there were originally many arms, so that each time they were sent out, they could not be heavy.
Generally speaking, a patient can find more than a dozen such metastatic lesions, each of which is different, which adds a second layer of difficulty to cancer treatment-genetic heterogeneity between metastatic lesions.
Similarly, no medicine can eliminate them all, and it is impossible to cut them off after transferring so much.
Difficulty 3. Creating New Arms when Small Troops Divide into Large Arms
In addition, there are third and fourth layers of difficulties in treating cancer.
You know, when cells divide, they will produce new mutations. In our metaphor, in the process of turning a small army into a million troops, many new arms will appear.
This results in many arms that are not heavy in each metastatic focus, and usually there are only a few arms that are resistant to drugs.
As a result, drug therapy is even more difficult, which is the third layer of difficulty.
Let’s give another example.
Many patients will use Cetuximab to treat colon cancer, However, most patients who use this drug will develop drug resistance after taking it for 5 to 11 months. Studies have shown that this drug resistance occurs in the process of cancer metastasis. What is more striking is that the drug resistance exists before taking the drug, but the proportion of soldiers who have this drug resistance ability before taking the drug is very small.
Difficulty 4. Each patient’s cancer corps has different arms.
The fourth level of difficulty is the difference between individuals.
Both Zhang San and Li Si have lung cancer, but their arms composition of lung cancer can be very different. As a result of these differences, drug A is useful to Zhang San, Zhang Sanyi takes it well, but it is completely useless to Li Si.
For chronic myeloid leukemia (CML), there is a very effective drug called Imatinib, which is also listed as one of the essential drugs in the basic medical system by the World Health Organization. However, this drug is not effective for everyone, only for Philadelphia chromosome positive (Ph + CML) patients (about 95%).
The above four difficulties are to explain why cancer is difficult to cure from a genetic point of view. In addition, there are many reasons such as environment, treatment methods, immunity, etc.
However, there is no need to be overly pessimistic about this. Since the [cancer war] began in 1971, our understanding of cancer has deepened a lot, and the survival rate of cancer is also increasing year by year. As mentioned earlier, the five-year survival rate of chronic myeloid leukemia increased from 31% in 1993 to 59% in 2009.
I believe that cancer, which is currently called “incurable disease”, will one day be conquered by us.