Cancer is characterised by uncontrolled cell growth. The word tumour comes from the latin word tumor meaning swelling. Tumours are either benign or malignant, and a malignant tumour is synonymous with cancer. Cancers are characterised by their ability for the cells to lose their attachment to the primary tumour and to spread to other parts of the body and this process is known as metastasising.
When a tumour metastasises, it does so either by direct spread to adjacent organs or via channels such as the blood vessels or more commonly the lymphatic vessels. Once these cells lodge in a distant organ they then continue to divide, this time developing a secondary tumour which, similar to the primary tumour, will eventually take over the function of that organ and kill the patient.
The vast majority of our cells are programmed to die within a certain time period and to be replaced by new cells. This programed cell death is known as apoptosis. However, for reasons that are not clear in most cases, this programed cell death does not occur when it should and the cells continue to divide in a haphazard fashion.
These old cells tend to develop genetic defects and whether these defects are the cause or the effect of the uncontrolled cell growth is not clear. Because of the genetic defects these cells do not function normally and produce proteins that are potentially harmful to the body. The other significant event is that the tumour, whether primary or secondary, eventually takes over the function of a particular organ and if this is an important organ such as the liver or lungs then the inevitable result is death of the individual.
The five commonest cancers that have the ability to metastasise and therefore to potentially kill the patient, in order, are lung, bowel, breast, prostate and kidney. So, these particular organs denote the site of the primary tumour. All five of these cancers have the propensity to metastasise to anywhere in the body but the commonest places are to the lungs, liver and bones.
With some cancers, we know the cause. For instance, we know that in the fast majority of cases of lung cancer the patient is either a smoker or an ex-smoker who has smoked for many years. It does arise in a few patients who have not smoked and in those is difficult to define a cause. In other types of cancer, the cause is less easy to identify.
So, for instance with bowel cancer we know that it is due to a series of gene defects, but we are not clear as to what actually causes the particular genes to become defective. And in fact, it may be a combination of causative agents including the possibility of an infective agent such as bacteria, virus or a chemical that has been released into the environment, or has found its way into our food chain.
The mainstay of treatment is to erradicate the primary disease before it has had an opportunity to metastasise. With all of these five cancers the initial treatment of the primary disease is surgical i.e. removal of the affected organ. It is an unfortunate fact that once a tumour has metastasised the chances of a patient being cured are dramatically reduced.
No amount of surgical intervention with the primary tumour will alter the course of the disease and all that one can hope for is that the symptoms related to the primary disease are negated or reduced by the surgery. It is then a matter of relying on a combination of other therapies, in particular chemotherapy or radiotherapy, to reduce the impact of the metastatic disease.
Chemotherapy is the use of drugs that target and destroy actively dividing cells such as is taking place within a tumour. Radiotherapy acts in a similar way but instead utilises ironizing radiation produced by radioactive isotopes to bring about the death of the dividing cell. Because these modalities target dividing cells within the cancer, they also target dividing cells within normal healthy tissue and this explains the side effects that patients can experience when being treated with this type of therapy and this includes things such as sterility, gastrointestinal disturbance and hair loss.
Undoubtedly with these cancers and the numerous others, management has to be centred around identifying the cause and preventing them if we are going to make any real headway with regards to reducing the incidence. Until that time, we are reliant upon the current modalities of treatment namely surgery for the primary disease and a combination of chemotherapy and radiotherapy for the secondary disease.
As far as the role of obesity is concerned, we know that with certain cancers in particular breast and bowel, they are more common in patients who are either overweight or suffering from obesity and that relationship tends to be linear with the actual degree of obesity. But because we do not know what causes the cancer in the first place it is very difficult to define how obesity might be acting to actually bring about this increase.
Nonetheless, because we have identified obesity as a risk factor, we are duty bound as individuals to reduce the potential risk of developing the disease by dealing with obesity itself. That is purely common sense and logic. And that is why as a cancer surgeon I am very passionate about all of my patients being informed of this risk, so that they may reduce their own personal risk of developing it later.
The role of autophagy, literally meaning the body eating itself, is an interesting concept in the management of cancer and its increased risk due to obesity. It is purely a hypothesis but one can certainly envisage the scenario of the body being denied its daily requirement of nutrients, at which point it identifies potentially harmful proteins, already in existence within cells for example, and then to utilise those damaged cells, for instance within a cancer, as a source of nutrient. So, in effect it is selectively using its bad cells as food.
The converse is where the body is being over-fed, or has more nutrient than it requires, as in the obese patient, at which point it has no requirement to use damaged cells for nutrition, thereby potentially allowing them to multiply unrestricted. So, the body’s inability to invoke autophagy as in the obese patient, might explain why cancer is more common in patients suffering from obesity. I should stress that this is purely a hypothesis.