In medical science, cancer is a malignant tumor originating from epithelial tissue and is the most common type of malignant tumor. Types of cancer etiology 1. Damage to genetic material Most likely, almost all growing cells in human body will become cancerous after long-term stimulation by physical factors or chemical factors. In other words, most cells will become cancerous only when they are damaged for a long time, more precisely, their genetic material, i.e. DNA in the nucleus, is damaged. For example, an acid splash on the hands will kill or damage some skin cells. Eventually, some of the damaged cells die and the dead cells detach from the skin. If the acid burn is severe, the skin will blister and become rough and uneven until finally the acne heals. The acid only kills the cells or damages the cell membrane, but it does not damage the genetic material inside the cells. In contrast, if you expose your hands (or your whole body) to strong sunlight every day, the damage to the genetic material of the skin cells will gradually increase. This is because sunlight contains several types of rays, and the ultraviolet rays in these rays are capable of causing chemical reactions in the nuclei of the body’s cells. Over time, the skin becomes cancerous. Ultraviolet light plays a key role in this cancer process. Similarly, cigarette smoke contains chemicals that damage the genetic material of lung cells, and they are the cause of lung cancer. Of course, not all harmful substances in cigarette smoke can cause lung cancer. For example, the substances that cause chronic bronchitis and emphysema are similar to the acid spilled on your hands mentioned earlier, which can cause damage but not cancer. Carbon monoxide in cigarette smoke can damage the heart, but does not cause cancer. The damage that can cause cancer (and not other diseases) is only damage to the nucleus of the cell, which is actually damage to the DNA in the nucleus. How genetic damage occurs 2. Predispositions and determinants It seems that some cells (more precisely, the nucleus) can become cancerous with very little damage. Some cells are almost already designed and behave programmatically. They become cancerous with little (almost no) external damage, while others seem to be strongly resistant.