Cancer… is a distorted version of our normal selves.
Harold Varmus, 1989
All cancers begin in cells, the body's basic unit of life. To understand cancer, it is important to understand how a normal cell in the body becomes a cancer cell.
The body is made up of trillions of living cells. Each cell in our body has a certain job to do. Normal body cells grow, divide, and die in an orderly fashion. They die when they are old or damaged, and then they are replaced with new cells.
However, sometimes this orderly process goes wrong. The genetic material (DNA) of a cell can become damaged or changed, producing changes(mutations) that affect normal cell growth and division. When this happens, cells do not die when they should and new cells form when the body does not need them. These extra cells may form a mass of tissue called a tumour.
Abnormal cell division could begin in any part of the body and at any time depending on the factors that cause the mutations. Cancer is therefore not just one disease but a group of diseases characterised by abnormal cells dividing without control.
It is important to note that tumours that form in the body are not always cancerous. Essentially, there are two types of tumors – Benign and Malignant. Benign tumors, often called as non-cancerous, are localised tumors that do not spread to other parts of the body. They might grow and be painful but do not invade into other body parts or tissues. As commonly said “they usually push the normal tissue to the side”. Some examples of benign tumors are moles, polys or cysts which may or may not require to be removed/treated.
On the other hand, malignant tumors are the ones that spread to other parts. They have the ability to invade organs and/or tissues that are close to the primary tumor (neighboring organs) or organs that are at a distance. This spread usually happens either through the circulatory system (blood) or the lymphatic system. This process is called metastasis. To sustain themselves through this journey they plunder the body’s normal sources of blood and oxygen depriving the body’s normal cells of their sustenance and in turn causing them to atrophy. Thus, something that begins as a normal bodily function could grow into something that harms the body itself. Cancer has therefore been called "a distorted version of our normal selves".
Further, tumors can be classified into solid tumors and hematological tumors. Solid tumors are clump of cells and do not contain any liquid or cysts. Solid tumors may or may not be malignant. Some common areas that a solid tumor can occur are in the bones, muscles and organs. Hematological tumors are the ones that happen in the blood cells or the bone marrow (blood forming cells) or in the cells of the immune system.
The question that bothers most of us is ‘what causes cancer?’ or ‘why does cancer happen?’ The answer is not yet definite, and it is difficult to say as to why one gets cancer and why one doesn’t. But research has shown that we are exposed to many risk factors that increase our chances of developing cancer. Broadly, these risk factors can be divided into two categories – avoidable and unavoidable factors. Avoidable factors are the ones that are under our control like exposure to harmful chemicals and other substances, lifestyle etc. and unavoidable factors are the ones that we cannot control like age, family history, hormones etc. For further information visit http://www.cancerclinics.in/what-causes-cancer
There are more than 100 different types of cancers. In order to make classification easier, most cancers are named for the organ or type of cell in which they start. For example cancers that begin in the breast are called breast cancer. Cancers that are named for the type of cell in which they originate are grouped into five main categories.
Carcinoma - cancer that begins in the skin or in tissues that line or cover internal organs. This tissue is made up of epithelial cells. There are different types of epithelial cells and cancers that begin in them have specific names. For example – cancers that begin in the epithelial cells that produce mucus or fluid are called adenocarcinomas. Cancers that begin in the lower layer of the epidermis are called basal cell carcinoma. Similarly we have squamous cell carcinoma and transitional cell carcinoma.
Some examples of carcinomas – adenocarcinoma of breast, adenocarcinoma of lungs, adenocarcinoma of stomach, basal cell carcinoma of skin, basal cell carcinoma of oesophagus, squamous cell carcinoma of throat, squamous cell carcinoma of the cervix.
Sarcoma - cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue. The most common type of bone cancer is osteosarcoma. Cancers that form in the cartilage, fat, muscles, blood vessels are commonly called as soft tissue sarcomas.
Some examples of sarcomas - sarcoma of bone, sarcoma of uterus, sarcoma of breast
Leukaemia - cancer that starts in blood-forming tissue such as the bone marrow and causes large number of abnormal blood cells to be produced and enter the blood. They do not form solid tumors. Leukemias can be categorised into four main types based on how aggressive the cancer is (whether it is acute or chronic) and the type of blood cell the cancer begins in (lymphoblastic cells and myeloid cells).
Examples - acute lymphoblastic leukemia, acute myeloid leukemia, chronic myeloid leukemia and chronic lymphoblastic leukemia.
Lymphoma and myeloma - cancer that begins in the cells of the immune system. Lymphoma is a type of cancer that begins in the lymphocytes (disease fighting white blood cells also known as the B-cells and T-cells) and myeloma is the cancer that begins in plasma cells. Hodgkin and Non-Hodgkin lymphoma are the commonly known types of lymphomas.
Sarcoma - cancer that begins in the tissues of the brain and spinal cord. They are primarily named after the cell in which the cancer is formed and the area where the cancer was first formed.
Some examples of cancers of central nervous system – brain stem glioma, medulloblastoma.