Cancer is an illness that will unfortunately affect most of us at some point in our lives – either directly or through someone we care about. The remarkable thing about cancer is that although in many ways the disease acts like a foreign invading body it is actually our own cells that have started to misbehave. When we look at how cancer cells operate they can seem crafty, clever and at times downright evil. Of course they’re not. They’re cells – unable to think or have any emotion-like behaviour. The thing that allows cancer cells to behave in the way they do is actually the same process that allowed human beings to evolve from single celled swamp-dwelling amoeba – genetic variation and adaptation.
Most cells in our body behave the way they should. When they get signals from the tissue surrounding them telling them to multiply they will divide into two new cells; when they get old or damaged they will kill themselves in a cell-suicide process called apoptosis. Cells are very altruistic in this way, they even have the good grace to package all their remnants into little membrane-bound sacks that other cells can come along and chow down on. Cancer cells are not altruistic. While normal cells function solely to benefit the organism as a whole, cancer cells have their own agenda and that is to stay alive and to keep dividing. The problem for our body is that when a cancer cell goes forth and multiplies uncontrollably, a mass of cells form and that mass is a tumour.
The cancer cells don’t set out to become harmful, the process is random. One of the first steps in a cell becoming cancerous can be losing the ability to divide properly. If genes that control cell division are mutated, cells may start to divide randomly and more often. But these types of mutations alone are not usually enough to cause cancer and other types of adaptations are needed.
Potential cancer cells become really dangerous when they not only divide in an uncontrolled way but also fail to recognise when they need to commit suicide. One of the main reasons a cell might normally commit suicide is because it has miscopied its DNA. Before a cell divides it has to produce an identical copy of its entire DNA so each of the two resulting ‘daughter’ cells will have a full set of genes. This is no easy task for the cell, as there is an estimated 3 meters of DNA crammed into each one. There’s a lot of room for mistakes and they do happen. Normally the cell will detect a mistake and either rectify it or if that’s not possible commit suicide. If the genes that control this detection or suicide process are mutated the cell will not kill itself and will pass faulty genes onto the two new cells. This means you now have cells that will continue to divide and easily accrue mutations, which is very bad news indeed.
The body has natural ways to keep cancer in check; one of these is our immune system. Because cancer cells don’t act normally our white blood cells often recognise them as different and attack them in the same way they would a bacteria or virus-infected cell. It is thought that the immune system can actually keep cancer cells in check for years, but eventually a cancer cell might gain a genetic mutation that allows it to evade the immune system. If this happens the cancer cell will thrive, multiply and produce many more cells that can avoid the immune response, meaning a tumour can grow more easily.
Within a tumour there is often very little blood supply and this means less oxygen and fewer nutrients reach the cancer cells, which can inhibit growth and even cause them to die. Unfortunately, some cancer cells gain mutations that allow them to release signalling molecules that encourage blood vessels to grow towards them. Once again, the adaptation through genetic changes helps the cancer cells to survive.
In the final stages of the transformation from a normal cell into a rogue cancer cell, the cancer cells often gain mutations that allow them to move. The cells that gain this ability can migrate out of the tumour to find pastures new. They move their way into the blood supply or lymphatic system and hitch a ride to the closest organ or tissue to set up a new colony. This is how cancer spreads through the body and tragically is one of the hallmarks of advanced cancer.
Cancer cells show the ability to adapt and thrive as individual cells at the expense of the body as a whole. The body provides environmental pressures in its natural safe guards against cancer. The cells that can adapt to these pressures through random genetic mutation will go on to divide and pass on these cancerous traits to more cells. Although understanding these processes can show how scary and seemingly persistent cancer cells are, it also helps us understand how the disease progresses.
The advances we have made in understanding cancer in the last 30-40 years are phenomenal. It has given rise to drugs that target cancer cells at all these different stages during their development. There is a long way to go in the treatment of cancer and since every type of cancer will have a different set of mutations, there is no wonder ‘cure-all’ drug. Despite this, in recent years there have been huge leaps forward in DNA analysis. It is not inconceivable that in the near future patients will be able to have the DNA of a cancer cell analysed to work out a personalised treatment plan targeting their cancer specifically. Ultimately our understanding of the cancer cells hyper-adaptability may hold the key to beating the disease all together.
Post by: Liz Granger