Rene Bernards is a scientist affiliated with the Antoni van Leeuwenhoek. He explains what smoking does to people’s cells. They mutate. Someone who smokes a pack a day for a year can count on 150 of those mutations—in every cell—in the lungs. That is apparent from international research. “The good thing about this research is that we can now provide molecular proof that smoking is the cause of cancer.”

Full disclosure: René Bernards is not involved with the recent and ground-breaking in-ternational research into the effect of smoking on mutations. Mutations that lead to can-cer. The senior scientist of the Antoni van Leeuwenhoek and professor of molecular car-cinogenesis at the University of Utrecht can thus discuss the importance of the research without any self-interest.

“We knew of course that smoking can cause cancer. Now we can—as a forensic re-searcher—also deliver proof of who the culprit was,” Bernards says. “Smoking leaves fingerprints in the DNA of cancer, in the form of specific mutations. We can now deter-mine what caused those mutations.”

The study was published in Science in early November. Researchers analyzed changes in the genes of more than 5,000 tumors. Cancerous tissue from the lungs, but also from 16 other organs for which it was suspected that smoking caused the cancer. On the basis of the nature of the mutations, the researchers noted that smoking led to various kinds of cancer.

Bernards: “If you look at my profession, then the troubling thing about a cigarette is that there are more than 60 carcinogenic substances in it. With a cell mutated by cancer, that makes it complicated to determine which substance caused the cancer. In this study, the researchers were able to establish the specific ‘fingerprint’ in the DNA that smoking left behind in the body. Amazingly good work. We suspected it already, but now we can de-liver the molecular proof that smoking is the cause of cancer.”

That also applies for non-smokers who develop cancer as a result of second-hand smoke. Thousands of them are included in the study. “That means that not only smokers, but also non-smokers can determine whether smoking has caused the cancer. They can also point a finger at the manufacturers.”

The research is also important with an eye to developing medications. “Damaging sub-stances enter the body through the lungs due to smoking. Those substances reach other organs through the blood. The fingerprint that smoking leaves behind was also found in tumors there,” Bernards says. In the future, these insights can contribute to targeted med-ications to combat the cell division.