## Why does cancer die when cells only divide?

Cancer involves actively dividing cells that, in advanced stages, damage healthy tissue, depriving it not only of space but also of the nutrients that healthy organs need. This causes the organ to stop functioning properly. There are many ways a tumour can damage the human body. If the digestive system is affected, the body cannot absorb nutrients and suffers from malnutrition. If the respiratory system is affected, the problem is that the body does not receive enough oxygen. Damage to the bones can result in too much calcium being released into the blood or weakened bones can break and fail to heal. The liver, in turn, has an irreplaceable role in eliminating toxins from the body, and when it cannot perform this function, the human body is exposed to poisoning. Damage to the bone marrow, in turn, does not allow the formation of a sufficient amount of blood cells, which leads to the development of anaemia, in which the red blood cells do not have enough time to supply the tissues with oxygen. If there are not enough white blood cells, the body cannot fight infections, the lack of platelets is dangerous in bleeding because the body cannot stop it. A brain tumour, in turn, can press on the centres of memory, speech, vision, or orientation, as well as vital control systems, such as the respiratory centre. In some cases, when the cancer can no longer be treated, the body gradually weakens, and the organs fail.

Pancreatic cancer is one of the deadliest diagnoses among all cancers. Approximately 95% of patients with this diagnosis die. The pancreas is a relatively small organ, but it performs a variety of functions. Pancreatic juice is secreted into the small intestine and helps digest proteins, fats, and carbohydrates. The organ is also important because it contains the Islets of Langerhans, which produce the hormones insulin and glucagon, which affect blood sugar levels. It is the weakening and loss of pancreatic functions that lead to a dramatic deterioration in the general health of patients. Part of the reason for the high mortality rate is that there are currently no sensitive methods for diagnosing pancreatic cancer, as the symptoms can be too general, so the diagnosis is often made at a late stage.

Each patient is an individual, and there are already many means to relieve the pain, eliminate the side effects of the disease, and, in the case of terminal illness, improve and prolong the quality of life through palliative care. Modern medicine saves lives, but cancer is still a challenge. While the development of modern medicine has had a decisive influence on the treatment of cancer, with its onset, a worsening of cancer incidence could be initially observed. This is the so-called paradox of modern medicine.

Society has undergone many changes in the last century, which have prevented many deaths. Thanks to this, a larger percentage of the population is growing old. And with increasing age, the risk of developing cancer also increases. With each cell division, the number of which is directly proportional to the lifespan, there is a certain number of DNA errors that occur and so the risk of developing cancer by chance increases, which is also different for different tissue types. It is the same as the lottery: someone who plays every week is statistically more likely to win than someone who plays once a decade. Therefore, in the colon, where cells are replaced every 2-5 days, the risk of developing colorectal cancer increases with age, and is greater than the risk of developing a tumour in the bones. Thus, the paradox is that despite the great advances of modern medicine in the treatment of many other diseases, society has not yet achieved the complete elimination of cancer, but on the contrary, more and more people develop it during their lifetime.

Fortunately, modern medicine also has the dream and ambition to eliminate cancer and has effective means for cancer treatment. Classical cytostatic drugs work on the principle of inhibiting cell division by damaging cell structures, damaging DNA and RNA, or altering metabolism. The problem is that these drugs act non-specifically since they target all dividing cells. Therefore, chemotherapy can also cause hair loss, damage to blood formation, or nausea. In addition to chemotherapy, radiation therapy based on ionizing radiation, surgical removal of the tumour, or (for some diagnoses) bone marrow transplantation is often used in combination. But targeted treatments are also on the rise, including biological treatment and personalized medicine.

The scientific organization International Cancer Genome Consortium for Medicine aims to identify the genetic cause of the 50 most common types of tumours. This would enable the personalised treatment of patients based on the genetic cause of cancer rather than whether it is breast cancer or colorectal cancer. For example, a drug that binds to the receptor HER -2 (receptor for human epidermal growth factor 2), which is involved in the development of breast and gastric cancer, is already being used. The target of personalized medicine is also the protein product resulting from the genetic rearrangement of the Philadelphia chromosome (Figure 9.7). In this process, the ends of chromosomes 9 and 22 are exchanged, resulting in a fusion gene consisting of genes for bcr ac-abl proteins. The part of the chromosome encoding c-abl contains the information for the formation of the proto-oncogene, and the other chromosome contains part of the information for bcr to cause its continuous expression. The proto-oncogene thus transforms into an oncogene, activating white blood cell division and causing the development of chronic myeloid leukaemia. The drug can inhibit the activity of ABL so that the cells stop dividing excessively.