It surprised me the other day to read that cancer is now the most common cause of death in NSW.  The latest statistics, which are for 2005, were recently released.  All of us health professionals have been banging on for so long about heart attacks and strokes killing more people than cancer, that we now need to shift our thinking.  So much work has been done on recognizing the risk factors for cardiovascular disease over the past 40 years, and so much money has been spend on public health programmes, that the results are now significant.

A lot of money has also been spent on researching cancer, yet there is still no 'cure'.  I recall my father telling me when I was a child how his own family doctor had said when he was about 15, that by the time he had grown up they would have found a cure for cancer.  The problem is, cancer is not one disease, but a collection of about 300 diseases.  What they all have in common is that they result from a piece of DNA in a cell somewhere going awry.  It therefore causes that cell to grow and reproduce in an abnormal manner.  Cancers are classified according to which type of cell they affect, and which organ they originated in, hence the wide variety of often confusing names.  When cancer is diagnosed, it is further classified according to how sophisticated the cell is and whether there has been any spread beyond the original site.  Each type of cancer has its own sub-classification, and there are often more than one, often eponymously named, such as the Gleeson Score for prostate cancer.

Even when cardiovascular disease killed more Australians than cancer, cancer seemed to be the disease that people most feared.  This still seems to be the case, at a time when more cancers than ever can be prevented, controlled or even 'cured' (which is usually defined as a 5 year disease-free interval).  Of the 34,000 people diagnosed with cancer in NSW in 2005, at least 63% can be expected to survive five years at least.  This figure would be higher, but is dragged down by lung and bowel cancer, which tend to have a lower survival rate as they tend to be diagnosed late.  The most common cancers at the moment for women are breast, lung and bowel, in that order, and for men, prostate, bowel, melanoma and lung.  Note that the most common occurring is often different to the most common cause of cancer mortality.   In men, lung cancer is the most common cancer mortality, followed by lung. 

Cancer diagnoses are increasing, partly because we are getting better at detecting them at an earlier stage, and partly because we are living long enough to develop the disease.  Cellular DNA is simply more likely to make 'mistakes' in any older body.  Cancer is very much a disease of the 'third age' : nearly 60% of cancers occur in people over 65.  While  we tend to remember  young people with cancer who make the headlines, these are relatively uncommon.  Only 40% of cancers occur between 15 and 65, and this figure is inflated by Australia's high incidence of melanoma in younger people.

What causes cancer is a million dollar question.  Once you start thinking about cancer as  not a single entity, it is easier to understand that it is multifactorial.  Causes that we know about are ionising radiation and ultraviolet light exposure. Exposure to some chemicals is well known to be linked, such as analine dyes and bladder cancer, and cigarette smoking and cacers of the lung, mouth and throat.  Often there is a long latency period between exposure and diagnosis, so it is harder to accept the causal link.  People often still say “my father got lung cancer but he hadn't smoked for 40 years, so it can't be that.'  It's now thought that about a third of cancers are lifetyle related, so genes,environmental exposure  and plain bad luck aside, it is worth trying to modify our lifestyles to prevent  whatever we can.  We all know someone who lived to be 100 on a diet of cigarettes, alcohol and dripping, but the single case is simply that. Anyone who delights in quoting such cases as evidence to support their own lifestyle, is nailing their ignorance of statistics to a mast and flying it high. Population statistics are much more powerful can give us powerful data to draw conclusions from, and as time goes on, more and more of this data is being accumulated.  

Just before Christmas, a major report, based on five years work was released.  Called 'Food, Nutrition, Physical Activity and the Prevention of Cancer', it was put together by a group of scientists from nine universities in four countries, working for the World Cancer Research Fund. I referred to this report in my article on alcohol a couple of issues back.  They looked at all the original research according to a specially developed standardised protocol.  It's findings are complex, but can be abridged fairly simply.

1. Obesity.  Obesity is a major cause of cancers of the oesophagus, colon and rectum, pancreas, breast, endometrium and kidneys.  Our body mass index (wt in kgs) over ht (in M squared) should be between 21 and 23.  In Australia and the UK the average BMI is about 27, and has been since the end of WW2.  The mean BMI has been increasing steadily in many newly industrialised countries, such as India and China, where being overweight was once unusual.

2. Alcohol increases the risk for cancers of the mouth, pharynx, larynx, colon, rectum and breast, and also causes cirrhosis, which predisposes to liver cancer. Globally, alcohol consumption is on the increase.  Men should not exceed two standard drinks per day, and women should have no more than one.

3. Fruit and vegetables.  These appear to protect against a number of cancers, including prostate and bowel, but it is unclear just which ones are protective, and why this is so.  The Australian recommendations are that we should eat five different vegetables per day and two fruits.  Most Australians eat only two or three, and intake of fresh F&V is highly inversely correlated with income.

4. Meat.  The researchers commented that the most surprising finding was that red and processed meat were convincingly linked to colo-rectal cancer.  On average, if you eat large amounts of red and processed meats you have a 30% increased risk of colorectal cancer compared to someone who eats little or none.  And the more meat you eat, the higher the risk.  They suggest on average you should eat no more than 300 g of red meat per week.  The average Australian man eats 700 g per week and the average female eats 500.  Interestingly, in the UK, those figures are 970 and 550, respectively.  They note that reducing red meat consumption is also good for the environment, because producing meat uses large amounts of land and water, but accept that red meat is a convenient and good source of dietary protein. Try to incorporate more fish and legume sources of protein, if possible.  Beans, lentils and soyabeans are excellent sources of protein and fibre.  Also, reduce the amount of processed and preserved meats, such as bacon, sausages, pate and salami that you eat.  The sulfites and additives in these seem to be carcinogenic in large amounts.

5. Exercise, apart from helping to reduce weight, seems to have anti-cancer properties in itself.  The report recommends 30 minutes of moderate exercise (such as brisk walking to a slight puffiness) per day until fit, then once fit, 30 minutes of vigorous or 60 minutes of moderate exercise per day.
   
   

Other recommendations are that foods high in folate, such as green leafy vegetables, may decrease the risk of cancer of the pancreas and diets high in calcium may decrease the risk of bowel cancer.