MEDICINE has done a great job of reducing deaths from heart disease and stroke but less so with cancer. Despite a four-decade war against the disease, one that has cost hundreds of billions of dollars, in America alone 1.7m people are diagnosed with it, and about 600,000 die annually. Why has cancer not been cured?
The main reason that cancer has been such a hard problem to tackle is a lack of basic understanding of the underlying molecular mechanisms that drive it. The first medicines to tackle cancer, chemotherapy, came about during the second world war when it was discovered that people exposed to nitrogen mustard, a chemical similar to mustard gas, had significantly reduced white-blood-cell counts. Researchers investigated whether these compounds could be used to halt the growth of rapidly dividing cells, such as cancer cells. Thus began an era of testing different chemical compounds to see if they would kill tumours. New drugs were discovered that acted on cancer, but this sort of science was not particularly revealing about the cause of cancer or why these treatments often only worked temporarily.
Much progress has been made since. Thanks to a much deeper understanding of cell biology and genetics, there exist today a growing number of targeted therapies that have been designed at a molecular level to recognise particular features specific of cancer cells. Along with chemotherapy, surgery and radiotherapy, these treatments—used singly and in combination—have led to a slow, but steady, increase in survival rates. Childhood cancers and breast cancers are much more curable now than they used to be. But there remains much work—and research—to be done: some of the most promising new cancer medicines are the product of our deeper understanding of how cancer cells mutate and escape removal by the body. Cancer is seen today less as a disease of specific organs, and more as one of molecular mechanisms caused by the mutation of specific genes. The implication of this shift in thinking is that the best treatment for, say, colorectal cancer may turn out to be designed and approved for use against tumours in an entirely different part of the body, such as the breast.
There is a great deal of promise from another new therapy, called immunotherapy, which harnesses the body’s own immune system to fight cancer. It has been successful in inducing long-term remissions of hard-to-treat cancers in about a third of patients in ongoing trials. An active area of investigation is to predict which tumors respond to this and other therapies on offer. The world has still not cured the many cancers that exist. But over the next five to ten years the era of personalized medicine could see enormous progress in making cancer survivable.