Cancer development

Every cell within your body contains the instructions for life in the form of DNA molecules made up of thousands of genes which instruct your body to make proteins. When your cells divide your DNA must be replicated in order for the two resultant cells to have the correct amount of DNA. Replication is very tightly regulated through multiple complex processes. We can liken the normal DNA replication within a cell to the ice state of water, there is a definite structure therefore the amount of disorder and entropy is low. While the accuracy of replication is high, as you age your cells undergo multiple rounds of replication, and errors in DNA known as mutations can occur. Occasionally these mutations can lead to the uncontrolled division of cells - this is cancer.

When a mutation occurs it can affect the function of the protein produced by that gene. There are genes that when mutated can work to promote cancer, these are known as oncogenes and make proteins that are involved in driving the division of cells. There are also genes that work as regulatory mechanisms within cells which control cell division and prevent cancer from arising, these are known as tumour suppressor genes (TSG). As you have two copies of every gene (one from your father and one from your mother) it requires two mutations or “hits” to fully inhibit a TSG function. An example of a TSG is the TP53 gene, this makes a protein named P53 which is referred to as “the guardian of the genome”. P53 becomes activated in response to abnormal signals in the cell and triggers a self-destruct mechanism known as apoptosis. When both copies of TP53 become mutated more mutations can occur within the cell, allowing it to become cancerous. This single cancer cell can be likened to the liquid water, as the genes within the cell have been altered leading to a breakdown in regulation of cell signalling, disorder has increased but is still contained within a single cell.

At this stage the cancer cell is usually recognised by the immune system, as specialised cells circle through the body looking for infected or abnormal cells. When the immune cells recognise odd-looking cells, they attack and kill the abnormal cells as a defence mechanism to keep the body healthy and well functioning. This is known as immunosurveillance. In an individual with a fully functioning immune system this process is usually successful, although this is not always the case. When immunosurveillance fails, a mass of cancerous cells known as a tumour can develop. As the tumour grows these cells now have to compete with each other for resources such as space to grow, or for nutrients such as oxygen. As the cancer cells divide some cells will acquire new mutations, meaning that within the tumour not all the cells will be identical. In a process similar to natural selection, cells that have advantageous mutations or features will survive and out compete other cells. The main population of cells are known as the dominant clone, and smaller cell populations are referred to as subclones. This fully formed tumour can now be likened to the gaseous state of water, as there are many cancerous cells with many different mutations leading to multiple gene signalling pathways to become altered promoting cell survival and uncontrolled growth. The amount of disorder and entropy has increased at each stage of cancer development and has reached its peak with multiple pathways deregulated in multiple cells.

The level of complexity does not stop there, as the cancer cells can evolve to have increased movement they can then enter and pass through the circulatory system, lymphatic system or body cavities in order to spread and grow within a new site, in a process called metastasis. When patients are given therapy to kill off the cancer cells, the effectiveness of treatment is dependent on the type of cancer the patient has and the stage they were diagnosed at. When treatment is given it may be effective at killing off the majority of cells within the tumour, however subclones can contain mutations which allow them to resist and survive the treatment. This small population of cells can then survive and grow into another tumour, this is known as a relapse. It is also becoming increasingly apparent that it is not just the cancer cells themselves that are important, new research suggests is also the cells which surround them that can aid the evasion of the immune system and can also affect treatment response.

The goal of treatment is to remove all the cancerous cells, similar to refreezing water to make an ice cube; the particles realign and order is restored. Research into cancer development mechanisms is vital to the design of therapies which are more effective.