INTRODUCTION Cancer (medicine), 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 second leading cause of death in adults in the
Western world, and is 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.
