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, leukemias 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.
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.
Occurance:
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.
HOW CANCER OCCURS:
A.GENE DEFECTS :-
In some people, however, there are also inherited gene defects that can give a potential cancerous cell a head start. Genes are made of deoxyribonulceic acid (DNA—the cell’s chemical “instruction manual”—see Nucleic Acids) and are found in the centre of the cell in structures known as chromosomes. Humans have 23 pairs of chromosomes and over 50,000 genes. If a chromosome is likened to a book, each gene is a paragraph; a fault in a gene may be likened to a misprint.
Every time a cell divides a copy is made of the DNA. Sometimes an error occurs and a new cell ends up with an altered gene—a mutation. If the mutation occurs in a gene that normally controls cell growth, that cell may acquire the potential to become a cancer cell.
A cancerous growth, or neoplasm, is therefore clonal—that is, all its cells are descendants of a single cell. These cells have escaped the control of the normal forces regulating cellular growth. Resembling embryonic cells, they are unable to differentiate or mature into an adult, functioning state. As these cells multiply, they may form a mass known as a tumor, which enlarges and continues to grow without regard to the function of the tissue of origin.
The body has ways of fighting back against mutations and a number of faults has to accumulate before a tumour develops. This can take a long time, which is why cancer is mainly a disease of older people; for instance, 95 per cent of bowel cancers occur in those over 50.
B.TUMORS:-
Almost all cancers form tumours, but not all tumours are cancerous, or malignant; the greatest number are benign (not threatening to health). Benign tumours are characterized by entirely localized growth and are usually separated from neighbouring tissue by a surrounding capsule. Benign tumours generally grow slowly, and in structure closely resemble the tissue of origin. In some instances they may endanger the patient by obstructing, compressing, or displacing neighbouring structures, as in the brain. A few benign tumours, such as polyps of the colon, may be precancerous.
C.INVASION AND SPREADING:-
The most significant attribute of malignant tumours is their ability to spread beyond the site of origin. Cancer may invade neighbouring tissues by direct extension or infiltration, or it may disseminate to distant sites, forming secondary growths known as metastases. The routes and sites of metastases vary with different primary cancers:
(1) When a cancer extends through the surface of the organ of origin into a cavity, cells may break away from the surface and become implanted on the surface of adjacent organs.
(2) Tumour cells may migrate into the lymphatic channels and be carried to the draining lymph nodes, or they may penetrate the blood vessels. Once in the bloodstream, the tumour cells are carried to the point at which the vessels become too small for the large tumour cells to pass. Cells from tumours of the gastrointestinal tract will be stopped in the liver. Later they may go on to the lungs. Cells from all other tumours will go to the lungs before being carried to other organs. The lungs and liver are therefore common sites of metastases.
(3) Many cancers tend to shed cells into the bloodstream early in their course. Most of these cells die in the bloodstream, but some lodge against the surface and penetrate the wall into the tissue. A few may find themselves in a favourable tissue in which they are able to survive and grow into a tumour. Others may divide only a few times, forming a small nest of cells that then remain dormant (a micrometastasis). They may remain dormant for many years, only to begin to grow again as recurrent cancer, for reasons unknown.
Cancer cells, even when widely disseminated, may retain the physical and biological characteristics of their tissue of origin. Thus, a pathologist can often determine the site of origin of metastatic tumours by microscopic examination of the cancerous tissue. Identification of tumours of the endocrine glands, for example, is simplified because they may produce excessive amounts of the hormone that is produced by the parent tissue. Such tumours may also respond to administration of the hormones that normally control that tissue.
In general, the less closely a cancer resembles its tissue of origin, the more malignant and rapidly invasive it tends to be; however, the rate of growth of a cancer depends not only on cellular type and the degree of differentiation from the tissue of origin, but also on various host factors. A characteristic of malignancy is tumour-cell heterogeneity. Because of the abnormalities of proliferation in tumour cells, they are more susceptible to mutation. With time, a tumour tends to become less differentiated and to grow more rapidly. It may also develop increased resistance to chemotherapy or radiotherapy.
Abnormal Cells and Cancer-
Cancerous cells usually become far different from the tissue from which they arise. The tumour pictured here, an ovarian teratoma, bears no resemblance to the normal tissue of the ovary. Tumours like these contain such foreign material as bone, hair, skin, or teeth.
There are various types of CANCER, but for now i am going to discuss of LUNG CANCER...
Well what is lung cancer then?
Cancer of the lung, like all cancers, results from an abnormality in the body’s basic unit of life, the cell. Normally, the body maintains a system of checks and balances on cell growth so that cells divide to produce new cells only when needed. Disruption of this system of checks and balances on cell growth results in an uncontrolled division and proliferation of cells that eventually forms a mass known as a tumor.
Tumors can be benign or malignant; when we speak of "cancer" we refer to those tumors that are considered malignant. Benign tumors can usually be removed and do not spread to other parts of the body. Malignant tumors, on the other hand, grow aggressively and invade other tissues of the body, allowing entry of tumor cells into the bloodstream or lymphatic system which spread the tumor to other sites in the body. This process of spread is termed metastasis; the areas of tumor growth at these distant sites are called metastases. Since lung cancer tends to spread, or metastasize, very early in its course, it is a very life-threatening cancer and one of the most difficult cancers to treat. While lung cancer can spread to any organ in the body, certain organs – particularly the adrenal glands, liver, brain, and bone - are the most common sites for lung cancer metastasis.
The lung is also a very common site for metastasis from tumors in other parts of the body. Tumor metastases are made up of the same type of cells as the original, or primary, tumor. For example, if prostrate cancer spreads via the bloodstream to the lungs, it is metastatic prostate cancer in the lung and is called lung cancer.
Picture of Lung Cancer
The principal function of the lungs is the exchange of gases between the air we breathe and the blood. Through the lung, carbon dioxide is removed from the body and oxygen from inspired air enters the bloodstream. The right lung has three lobes while the left lung is divided into two lobes and a small structure called the lingula that is the equivalent of the middle lobe. The major airways entering the lungs are the bronchi, which arise from the trachea. The bronchi branch into progressively smaller airways called bronchioles that end in tiny sacs known as alveoli, where gas exchange occurs. The lungs and chest wall are covered with a thin layer of tissue called the pleura.
Lung cancers can arise in any part of the lung. Ninety to 95% of cancers of the lung are thought to arise from the epithelial, or lining cells of the larger and smaller airways (bronchi and bronchioles); for this reason lung cancers are sometimes called bronchogenic carcinomas. Cancers can also arise from the pleura (the thin layer of tissue that surrounds the lungs), called mesotheliomas, or rarely from supporting tissues within the lungs, for example, blood vessels.
