Under the Microscope: Over the course of most of my lifetime humanity cowered under the profoundly depressing symbol of the mushroom cloud, threatening the end of civilisation and, possibly, the end of life on earth. Thankfully that symbol has largely disappeared, writes Prof William Reville
Unfortunately there is no shortage of lesser fears to haunt us. One such is fear of the killer disease cancer. In this article, the first of two columns on cancer, I will briefly summarise the nature and history of the disease. Next week I will describe a new approach to cancer treatment that offers great hope for the future.
Cancer is as old as humanity. In 1932 Louis Leaky found a probable malignant tumour (possibly Burkitt's lymphoma) in the remains of the hominid Homo erectus. The oldest description of cancer, breast cancer, dates to ancient Egyptian papyri written between 3,000 and 1,500 BC.
Hippocrates, the "Father of Medicine", first recognised the difference between benign and malignant tumours. He coined the term cancer, because the swollen blood vessels around malignant tumours reminded him of crab claws and he named the disease karkinos, the Greek name for crab. This translates in English to carcinoma (cancer that forms on skin or on the cover of internal organs) the most common type of cancer.
Normal body cells grow, divide and die in orderly succession. When a person is young normal cells divide rapidly to facilitate growth. In an adult most normal cells divide only to replace worn-out or dying cells, or to repair injury. There are many types of cancer, but they all represent abnormal cells that are growing out of control. Cancer cells outlive normal cells, continuing to grow and divide forming new abnormal cells.
Normal cells can turn cancerous when their DNA suffers damage. DNA is the hereditary material of the cell, duplicating itself every time the cell divides, and it also directs the day to day activities of the cell. DNA is susceptible to damage from several sources - mistakes during duplication, damage from environmental agents such as tobacco smoke, interaction with viruses that invade the cell, and so on.
Cancer cells can undergo metastasis, which means they can migrate from their site of origin and move to other parts of the body where they continue to grow, interfering with normal tissue - eg breast cancer can migrate to the liver. Cancer cells can move from one place to another through the bloodstream or the lymph vessels. Cancers usually grow as solid tumours, but some types, eg leukaemia, are not tumours but are cancers of blood cells and blood forming organs and circulate through other tissues. Different types of cancer (eg of lung and breast) behave differently and respond to different treatments. Some tumours are benign (non-cancerous). They do not metastasise and are rarely life-threatening.
Cancer is a huge problem. About one in three of us will develop cancer during our lifetimes. Globally more than 11 million people are diagnosed with cancer annually and this may rise to 16 million by 2020. Cancer is the second leading cause of death (cardiovascular disease is the first) in developed countries, causing seven million deaths annually (1.7 million in EU), ie about 20 per cent of all deaths. The burden of cancer on society is big in every way, both on a personal and on the national economic level. More than 30 per cent of people diagnosed with cancer suffer clinical depression. In 2002, the estimated cost of cancer in the US reached $172bn.
Since cancer was discovered attempts have been made to devise treatments to defeat it. However, as the mortality statistics show, we still have a long way to go. Surgery was the first technique to have some success with cancer. John Hunter, the 18th-century Scottish surgeon, suggested that some cancers could be cured by surgical removal if they had not invaded adjacent tissue. Surgery developed greatly over the next century, spurred on by the development of anaesthesia.
Towards the end of the 19th century, William S Halsted developed radical mastectomy at Johns Hopkins Medical School in Maryland. Halsted's conviction that comprehensive local removal of a tumour would provide a cure was the basis for cancer surgery for the best part of a century.
English surgeon Stephen Paget (1855-1926) first recognised that cancer could spread around the body via the bloodstream, thereby limiting the effectiveness of cancer surgery. This led to the development of treatments after surgery to destroy any remaining cancer cells.
In 1895, X-rays were discovered by the German, Wilhelm Conrad Roentgen. It was soon noted that small daily doses of radiation over several weeks was useful as a treatment for cancer. Technology today allows radiation therapists to precisely aim radiation at malignant tumours and to minimise irradiation of adjacent healthy tissue.
Chemotherapy, the chemical treatment of cancer, was accidentally discovered during the second World War when the US military noted that nitrogen mustard, under study in an attempt to develop protection against mustard gas, also had marked activity against lymphoma - cancer of the lymph nodes. Since then, many chemotherapeutic chemicals have been developed, some capable of controlling cancer for long periods.
Today numerous new treatments have been developed to deal with cancer. I will discuss these approaches next week, concentrating in particular on a new drug that works by starving malignant tumours of their blood supply.
There is much optimism among cancer specialists that the new approaches will soon transform cancer from its familiar status as a killer to that of a chronic but manageable condition.