Jeremy Laurance: President's promise suggests his vision is simplistic

Four out of every 10 people living today will develop cancer at some point in their lives. Year after year, the incidence continues to rise despite all efforts to curb it, driven by the ageing of the population and factors such as increasing obesity and alcohol consumption. But just as the incidence of cancer has risen, so has our ability to treat it successfully.

Analysis of cancer patients between 1988 and 1990 and again between 1997 and 1999 shows there have been significant improvements in the numbers of patients who are considered to be cured of their cancer and go on to enjoy a similar life expectancy to the rest of the population. During this time, for example, the number of patients estimated to be cured of bowel cancer has risen from 42 per cent to 49 per cent. Similarly, cure rates for lung and stomach cancer have risen from 6 per cent to 8 per cent and from 15 per cent to 18 per cent, respectively.

The key to curing cancer is to catch it early, before it has spread outside the breast or bowel or prostate where it is located. For solid tumours, surgery is needed to remove the cancerous tissue followed by chemotherapy and radiotherapy to mop up any remaining cancer cells.

It is here that there has been real progress over the past 30 years with big improvements in survival rates. Skilful surgery has cured more cancer than chemotherapy and radiotherapy combined.

It is when cancer has spread that it becomes harder to treat – outside the "primary" organ such as the breast or prostate to the bones, brain, lungs or liver. Then survival rates are low and here progress in recent decades has been disappointing. Cancers that have spread are too late for surgery or radiotherapy and the only treatment is drugs.

"Curing" cancer therefore depends ultimately on developing effective drugs. That, in turn, depends on understanding the mechanisms of the disease at the cellular level. Yet despite decades of research and the expenditure of billions of pounds, successes have been limited.

Herceptin was hailed as a major advance against breast cancer, when it was launched in 2006, but it only extends survival by months, not years. It was seen as a major advance because even that limited gain was a dramatic improvement on other drugs.

Future gains will come from more basic research into the nature of the disease. Professor Sir Richard Peto, Britain's foremost cancer epidemiologist, who is based at Oxford University, said plans to sequence the genomes of 20,000 cancers would yield significant insights.

"There is a realistic prospect that the biology of cancer will be better understood. The pursuit of fundamental understanding is in the long run going to be the way forward. We are in an era now when it should be possible to understand the mechanisms by which cancer cells differ from normal cells and there will be therapeutic opportunities arising out of that."

Cancer is not a single disease and President Obama's promise to cure it suggests his vision is overly simplistic. There are at least 200 different types of cancer and as understanding of the processes deepens, what are today regarded as single cancers, such as breast cancer, may in future be understood as a collection of different cancers, each treatable with different drugs according to their differing natures at the molecular level.

There will be no magic bullet that will cure all cancers. The war against the disease in the US and Britain will be extended and difficult. Obama has promised a cure for cancer "in our time". He may need to live to a grand age.