As early as the end of the 18th century, the London physician Percival Pott observed that men who had worked as chimney sweeps in their youth developed testicular cancer more often than the average population. Although such observations about links between (occupational) contact with certain substances and cancer became more frequent, this finding did not catch on right away.
Chemicals promote cancer
In 1918, two Japanese scientists succeeded in proving beyond doubt for the first time that cancer can be triggered by chemicals: they coated rabbits with tar, which gave them skin cancer. Today, millions of smokers suck said tar from their cigarettes into their lungs every day, which is why lung cancer is the number one cause of cancer-related deaths. Men get it more often than women. However, the rate of disease in women is steadily increasing, due to changes in smoking behavior. Many other chemicals are also capable of causing cancer.
Radiation can trigger cancer
Radiation, such as ultraviolet (UV) light or X-rays, can also cause cancer, as was shown not long after the discovery and use of X-rays. Numerous technicians and scientists who worked with the new method of transilluminating bodies developed cancer. Marie Curie, the two-time Nobel Prize winner and co-discoverer of radioactivity, also had this painful experience. She died of leukemia, a cancer of the blood triggered by her long exposure to radioactivity. Chemicals and radiation also act by altering genetic information: Chemicals interact with the large molecule that is our genetic material, DNA. They alter it chemically and thus also cause a change in the information content. The rays have the same effect: They can alter individual “letters” of our genetic alphabet or cause the information to be torn apart.
Ames test examines substances for their carcinogenicity
These connections are also made clear by a test devised by American scientist Bruce Ames: He evaluated whether or not chemicals cause cancer by treating bacteria with them. These cannot get cancer, of course, but the chemicals cause changes in the genetic material of the bacteria that can be measured. A substance that has a strong mutagenic effect in bacteria also has a carcinogenic effect in humans. The so-called Ames test is still used today to find out whether a chemical is carcinogenic (= causes cancer) or not.
Also an “infectious disease”?
That cancer can also be “infectious” was recognized by one of the early cancer researchers, Francis Peyton Rous (1879-1970). He infected chickens with a liquid he had isolated from chicken ulcers. The (previously healthy) chickens also developed cancer. But it took some time before the cause was identified. It was a virus, which in this case had a cancer-causing effect. In humans, viruses are now also known to cause cancer under certain circumstances: These include HPV (human papillomavirus), which is responsible for the development of warts. In addition, certain papillomaviruses are probably responsible for the development of cervical cancer in women. The hepatitis B virus (HBV), on the other hand, triggers liver cancer. The reason for the cancer-causing potential of these viruses lies – again – in an alteration of the human genome: in this case, it is changed by the mere presence of the virus. The latter enters the human cell and adds its own (viral) genetic material to that of the human. This can, in various ways, upset the control system that “builds” the cell into its environment so that it begins to proliferate.
Can you inherit cancer?
The seamstress of American pathologist Aldred S. Warthin reported to him at the end of the 19th century that she was dying 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 propensity to develop cancer exists in certain families is thus older, but could only be recorded more precisely in the second half of the 20th century.Here, too, changes in the genetic makeup are the fly in the ointment: if such a change is already present in a family, this increases the probability that a disease will occur. Depending on which section of the genetic material is altered, very different cancer syndromes can be inherited. The best known is hereditary breast cancer, but numerous other organs can also be affected.
Lots of research, little therapy?
Cancer is the third leading cause of death in industrialized nations after cardiovascular disease and accidents. Research on the disease has been ongoing for many decades, and tremendous amounts of money have gone into this research. Yet the disease is still considered incurable in many cases. So why is it that so much is now known about the disease, but it still cannot be cured? 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 genetic material of the defective cells. However, this proves to be very difficult, since so many different changes can occur, and it is also technically hardly possible at present to specifically treat individual cells with the corrected genetic information. Another starting point for therapy would be to specifically destroy the wildly proliferating, defective cells. This is precisely what is done in a surgical procedure. However, it is much more difficult to do this with a drug. This is because while bacteria can be killed by antibiotics without serious side effects on humans, since they are (biologically speaking) very different from human cells, cancer cells are very similar to them. Therefore, a substance that severely damages the cancer cell will also severely attack the healthy cells. This is also the reason why many cancer drugs have such strong side effects. There will therefore still be some research to be done before all the different types of cancer are treatable.
