Environmental factors as a trigger: living consciously means avoiding cancer
By the end of the eighteenth century, Percival Pott, a London physician, observed that men who had worked as chimney sweeps in their youth were more likely to suffer from testicular cancer than the average population. Although such observations on relationships between (occupational) contact with certain substances and cancers accumulated, this finding did not prevail.
Chemicals promote cancer
In 1918, two Japanese scientists successfully demonstrated for the first time that cancer can be triggered by chemicals: they smeared rabbits with tar, causing them skin cancer.
Today, millions of smokers are sucking said tar from their cigarettes into their lungs every day, making lung cancer number one in cancer-related deaths. Men are more likely to get sick than women. However, the incidence rate in women is increasing continuously, due to the changed smoking behavior.
Many other chemicals are also capable of causing cancer.
Radiation can cause cancer
Also, rays such as ultraviolet (UV) light or X-rays can cause cancer, as shown not long after the discovery and use of X-rays. Numerous technicians and scientists working with the new method of screening bodies fell ill with cancer.
This painful experience was also made by Marie Curie, the two-time Nobel laureate and co-discoverer of radioactivity. She died of leukemia, a cancer of the blood caused by her long exposure to radioactivity.
Chemicals and radiation also act by altering the genetic information: the chemicals interact with the large molecule that is our DNA, the DNA. They change these chemically and thus also cause a change in the information content.
The rays work just as well: they can change individual "letters" of our genetic alphabet or lead to a ripping apart of the information.
Ames test examines substances for their carcinogenicity
These relationships are also clear from a test that the American scientist Bruce Ames has devised: He assessed whether or not chemicals cause cancer by treating bacteria with them. These, of course, can not get cancer, but the chemicals cause changes in the DNA of the bacteria that can be measured. A substance that has a strong mutagenic effect on bacteria also has a carcinogenic effect in humans.
The so-called Ames test is still used today to find out whether or not a chemical is carcinogenic (= carcinogenic).
Also an "infectious disease"?
One of the early cancer researchers, Francis Peyton Rous (1879-1970), recognized that cancer can also be "contagious". He infected chickens with a liquid he had isolated from chicken stings. The (previously healthy) chickens also got cancer. But it took some time for the cause to be recognized. It was a virus, which in this case was carcinogenic.
In humans, viruses are now also known that can trigger cancer in certain circumstances: These include the HPV (human papillomavirus), which is responsible for the formation of warts. In addition, certain papillomaviruses are likely responsible for the development of cervical cancer in women. The hepatitis B virus (HBV) triggers liver cancer.
The reason for the cancer-causing potential of these viruses is - again - in a change in the human genome: in this case, it is changed by the mere presence of the virus. This penetrates into the human cell and adds its own (viral) genetic material to that of man. This can confuse the control system that "installs" the cell into its environment in various ways, causing it to proliferate.
Can you inherit cancer?
The seamstress of the American pathologist Aldred S. Warthin reported at the end of the 19th century that she would die of cancer because all her family members suffered this fate. In fact, the woman died of the disease at a relatively young age. Warthin reported on her family, which he called the "cancer family." The idea that a tendency to contract cancer exists in certain families is thus older, but could not be grasped until the second half of the 20th century.
Here, too, changes in the genetic make-up of the hare in the pepper: If such a change already exists in a family, this increases the likelihood that a disease will occur. Depending on which section of the genome is altered, very different cancer syndromes can be inherited. The best known is the hereditary breast cancer, but many other organs can be affected as well.
Much research, little therapy?
Cancer is the third leading cause of death in the developed world after cardiovascular disease and accidents. For many decades, the disease has been researched and enormous funds have flowed into this research. Nevertheless, the disease is still considered incurable in many cases. So why do you now know so much about the disease, but still can not cure it?
Two reasons play a role here: the first is that cancer is triggered by a defect in the genetic material. The most obvious solution would therefore be to correct the genome of the defective cells. However, this proves to be very difficult, since so many different changes can occur and it is technically still barely possible to specifically treat individual cells with the corrected genetic information.
Another starting point for therapy would be to deliberately destroy the proliferating, defective cells. This is exactly what is done in a surgical procedure. With a drug, however, it is much harder to do this. Because while bacteria can be killed by antibiotics without serious side effects on humans, since they (biologically considered) are very different from human cells, cancer cells are very similar to these.
A substance that causes serious damage to the cancer cell will therefore strongly attack the healthy cells as well. This is also the reason why many cancer drugs have such strong side effects. So there will be some research to do until all the different cancers are treatable.