Dr Ed Cheeseman, Consultant Paediatric Pathologist and Chair of CCLG’s Biological Studies Steering Group, explains the difference between ‘normal’ cells and cancer cells, how the latter develop, and what they do to the body.
What do normal cells look like and what do they do?
The human body is made up of many trillions of cells that together, form the various organs and tissues of the body, as well as circulating blood cells. The brain, for example, is made up of neurons (which transmit nerve signals), glial cells (which support the neurons) and other supporting cells such as the cells that form the blood vessels. Almost all cells contain a nucleus, which stores most of the cell’s DNA. DNA stores all of the genetic information that’s required for our development, function and reproduction. The DNA is almost exactly the same in every single cell, but the way it’s expressed varies between different cell types. Genes are made up of a specific length of DNA, and each gene codes for a particular protein. Proteins are the building blocks of our organs and tissues.
How do normal cells develop over time?
Normal cells go through a life cycle of being formed by division of a parent cell, growth, function (depending on the particular organ), division (to form new cells) and, finally, death, to be replaced by younger cells. The body has many ways of controlling this life cycle of cells, to ensure that the cells do not deviate from this normal pathway.
Unfortunately, things sometimes go wrong for various reasons, and then some cells escape from the body’s normal control mechanisms. These cells have the potential to become cancer cells.
What do cancer cells doand how does treatment target them?
Cancer cells have the ability to ignore the body’s signals that tell them to stop dividing, so that they can divide uncontrollably, forming a ‘lump’ of cancer cells. Instead of growing to a particular size, individual cells can again ignore the body, and become much bigger than normal cells.
Unlike normal cells that are kept safely where they belong, cancer cells have the ability to escape and move to different parts of the body. This is called ‘metastasis’, and is one of the defining features of cancer. Some cancer cells develop the ability to trick the body. For example, they can promote the growth of small blood vessels to feed them, and this allows them to grow even further. Or, they can bypass the body’s protective immune system that normally kills cancerous cells.
Oncologists can take advantage of these mechanisms, with some cancer drugs preventing the formation of new blood vessels, thereby starving the cancer cells of vital nutrients. Other cancer drugs target the cells of the immune system, so that they become reactivated against the cancer cells.
How do cells become cancerous?
There are several ways in which a normal cell can become a cancer cell. One of the more common ways is through damage to the DNA within the cell, often as a result of exposure to damaging environmental agents such as cigarette smoke or radiation. This often requires prolonged exposure to the damaging agent over a number of years, and therefore cancers that develop in this way tend to be more common in adults. Alternatively - and more common in children - cancer cells can develop due to random faults that occur in the DNA when cells divide, or due to faults in the DNA that have been inherited from one or both parents. All these changes in the DNA are called mutations.
Mutations in genes that regulate the normal life cycle of the cell can result in uncontrolled cell division. Similarly, mutations in genes that normally prevent the growth of cancerous cells, can also result in growth and division of cancer cells. There’s a group of genes that are responsible for editing mistakes that occur in our DNA, and if a mutation occurs in one of these genes, then the body loses its ability to fix or remove erroneous DNA, and cells with this abnormal DNA can continue to divide in an uncontrolled manner.
What are the commonalities and differences between cancers, and what does that mean for treatments?
Cancer is not one disease. In fact, there are hundreds of types of cancer, depending on what cell type the cancer has arisen in. Despite this diversity, there are some common features that most cancers share, such as uncontrolled cell division and growth, evasion of the immune system, and the potential to metastasise, or spread to different parts of the body. These common features form the basis for many cancer treatments.
Each individual’s cancer is unique to them, and this has led to more advanced treatments that are targeted to the individual, and based on the molecular characteristics of that person’s tumour cells. This is a new and exciting area in oncology, which has become known as ‘precision medicine’.
Why are cancers named what they are?
Cancers are usually named based on the organ or tissue in which they develop. The most common cancers in adults are carcinomas, and they arise in organs like the breast, prostate or lung, and they are called breast carcinoma, prostate carcinoma or lung carcinoma (although subtypes occur even within each organ). In children, cancers more commonly arise in the brain or spinal cord, the blood (leukaemia), and bone and soft tissues (sarcomas: for example, osteosarcoma and rhabdomyosarcoma). Other common childhood tumours include Wilms’ tumours that arise in the kidney, and neuroblastoma that arises in nerve cells. In some rare cancers, we don’t know for certain which cell type or tissue the tumour has arisen from, such as Ewing sarcoma.
