Smoking and cancer
Lung cancer is a disease were abnormal cells in the lung grow uncontrollably, causing them to form tumours. Lung cancer is one of the more common forms of cancer in the UK with 46.388 cases in 2015 alone. The primary cause is smoking, but it can also be caused by polluted air, radon, ionised radiation, asbestos, arsenic, tuberculosis, and compounds from certain work environments. Patients can exhibit symptoms like persistent coughing, coughing up sputum, frequent diseases in the airways, difficulty breathing, hoarseness, and chest pains.
Smoking not only causes cancer in the lungs, but can also cause cancer in other organs, such as the bladder. This is because tobacco smoke is inhaled, and the lungs then transport the chemicals in the smoke to the bloodstream, along with oxygen, where it is distributed to the rest of the body. Smoke from tobacco contains more than 70 different carcinogens and is in fact the most potent cancer developing factor in our environment that we know of.
Genetic changes result in cancer
But how and why does tobacco cause lung cancer? The same question was asked by the scientists from John Hopkins Kimmel Cancer, and they found out that approximately 85 % of lung cancer cases are caused by smoking, and as the number of smokers decline, the number of lung cancer cases also decline.
The scientists examined important factors in the cells’ behaviour called ‘epigenetic’, which is a factor that can change the way our genes are expressed. Genes are composed of DNA, which is codes for different proteins, produced by our cells. These proteins enable the cells to perform a range of functions, e.g. are proteins used to create hormones or break down fat. The epigenetic changes occur in the genes and result in an over- or underproduction of the protein the specific genes codes for. This is because epigenetic changes can ‘turn off’ or ‘turn on’ genes within the cell’s nucleus.
In the study, the scientists explained that it is believed that cancer is caused by a complex process, involving both genetic and epigenetic changes. These changes could be caused by different forms of stress within the cell.
Research confirms that smoking causes epigenetic changes
In their study, the scientist extracted cells from the airways and bathed them in a liquid form of tobacco smoke every day for 15 months. This is comparable to 20-30 years of smoking 1 or 2 packs a day. After just 10 days, the scientists were able to see that the cells were more damaged than the cells that were not exposed to the smoke. The type of damage to the cell was similar to the type of damage that some harmful oxygen containing molecules have on genes. These oxygen containing molecules are present in tobacco smoke.
After 3 months, the scientists were able to measure a significant change in the cells. There was a change in the composition of the hormones in the cell that are necessary in avoiding a cell becoming a cancer cell. The hormones could affect epigenetic changes, which turn off the genes protecting the cell from becoming a cancer cell. It was especially genes that prevented the cell from dividing uncontrollably. Additionally, genes stimulating the cell to divide were more active, meaning there was an excess of proteins being produced by these genes; however, the genes were not damaged. These overactive genes are the same ones we know to be damaged in lung cancer patients.
If the scientists damaged the genes, the cells only became cancer cells if they were affected by epigenetic changed beforehand, meaning that the cell had to be subjected to 15 months of liquid tobacco smoke before the damage resulted in cancer. The scientists have a theory that smokers who quit can reduce the degree of epigenetic changes in their genes, thereby reducing the risk of damage to their genes, which then reduces the risk of lung cancer. Former smokers have more epigenetic changes than those who does not quit smoking.
However, it remains unknown exactly how epigenetic changes affect the genes and how this is linked to the development of malignant tumours in the lungs. A number of different medications, which are capable of removing some of these epigenetic changes in our genes exist, and these medications are in the process of being tested for their effect on the early stages of leukaemia. Hopefully, this knowledge of tobacco smoke’s effect on the airways will enable us to discover new types of medication, which will be capable of counteracting the damage, and thus reduce the risk of lung cancer.
