Cancer

I

Introduction

Cancer, new growth of tissue resulting from a continuous proliferation of abnormal cells that have the ability to invade and destroy other tissues.

Cancer, which may arise from any type of cell and in any body tissue, is not a single disease but a large number of diseases classified according to the tissue and type of cell of origin. Several hundred such classes exist, constituting three major subtypes: The first, sarcomas, arise from connective and supportive tissue, such as bone, cartilage, nerve, blood vessels, muscle, and fat. The second, carcinomas, which include the most frequently occurring forms of human cancer, arise from epithelial tissue, such as the skin and the lining of the body cavities and organs, and glandular tissue, such as that of the breast and prostate. Carcinomas with a flaky structure resembling skin are termed squamous-cell carcinomas. Those that resemble glandular tissue are called adenocarcinomas. The third subtype, leukaemias and lymphomas, include the cancers that involve blood-forming tissue and are typified by the enlargement of the lymph nodes, the invasion of the spleen and bone marrow, and the overproduction of immature white blood cells.

II

Prognosis and the Long-Term Picture

Many people are now successfully treated for cancer. For example, it is estimated that, out of more than 5 million Americans who have had cancer, 3 million have survived more than five years, and nearly all the survivors can be regarded as cured. The modern approach to cancer treatment also includes an emphasis on the patient’s quality of life—both physical and mental.

There are many forms of cancer where the chances of survival are many times better than they were just a few years ago. Developments in the field of children’s cancers are perhaps the most encouraging. For instance, 90 per cent of children recover from Hodgkin’s disease, whereas 30 years ago only about half survived. Other forms of cancer, such as non-Hodgkin’s disease, some leukaemias, and testicular cancer, can be successfully treated, as can certain forms of non-invasive bladder cancer, which, if detected early, can be contained over a period of several years.

The death rate from cancer has fallen progressively in people under 50, probably because healthier habits and environment have reduced prolonged exposure to carcinogens. Earlier diagnosis, which is absolutely vital in all cases, and improved treatments are also involved. This drop is expected to extend to older age groups as these younger people age.

Decreases in the number of smokers in some countries are starting to have an impact on the cancer figures. For instance, in the United Kingdom the number of deaths from lung cancer in men has finally started to decline. Unfortunately, the number of women dying from it is still going up; Scottish women have the highest rate of death from lung cancer in the world.

The overall risk of death from cancer has increased over the past 30 years. This is because cancer is mainly a disease of older age and, as greater success is achieved at preventing early deaths from other illnesses such as heart disease, more people are living long enough to reach an age where their cancer risk increases.

III

Occurrence

Cancer is the leading cause of death in adults in the United Kingdom and the second leading cause of death in adults in the rest of the Western world. In the United Kingdom in 2002 it was responsible for 155,180 deaths; it is also one of the leading causes of death from disease in children between the ages of 1 and 14. However, despite this, it is still rare in young people. In the United Kingdom cancer affects about 1 in 650 children.

The age-adjusted death rate per 100,000 population from all cancers in males is 246.5 in Hungary (one of the highest), as compared to 83.5 in Mexico (one of the lowest). For women, it is 139.8 in Denmark and 62.3 in Mauritius. The rates for England and Wales are 179.2 for males and 125.7 for females; in the United States, the rate is 164.4 for men and 110.6 for women. For particular cancers, the difference between countries may be as high as 40-fold. Evidence from studies of populations that have migrated from one geographical area to another suggests that these variations are due to differences in lifestyle rather than ethnic origin. This is consistent with other evidence that most cancers are predominately related to environmental causes rather than heredity, although the two may interact.

The cancers that cause the most deaths in Europe and the United States are those of the lung, bowel (colorectal), breast, prostate, and stomach. Together they account for about half of cancer deaths. These are also the most common types of cancer along with skin cancer. Skin cancer is the first or second most common cancer in many Western countries such as the United States, Australia, and the United Kingdom. Fortunately, with the exception of malignant melanoma (the rarest and most serious form), skin cancers are rarely fatal.

IV

How Cancer Occurs

Cancer is a multi-stage process where a series of irreversible genetic errors occur in a cell in the body during a patient’s lifetime. The early stages (initiation) are critical for setting the process off. Later changes lead to spread and increased growth rate, and are triggered by a range of external factors, known as promoters. These errors may happen because the person has been exposed to cancer-causing agents (carcinogens). For instance, cigarette smoke contains many chemical initiators and promoters.