There are over 100 different types of cancer. It can affect almost any organ in the body from the skin to the colon. The most common forms of cancer in North America are lung cancer, breast cancer, and prostate cancer. There are four major groups of cancers:
As someone's body grows, certain cells divide and multiply to create new tissue, while other cells (like muscle or nerve cells) do not divide and multiply. The body has specific genes called oncogenes that control the ability of cells to divide and grow. Genes called tumour suppression genes tell the cells to stop dividing. Cancer occurs when either the oncogenes are "turned on" when they aren't supposed to be, or the tumour suppression genes are "turned off" when they're supposed to be on. This results in excess growth in the form of tumours.
Cancer cells go through different stages as they divide and multiply to form a tumour. At first, normal cells divide faster than they should and the total number of cells increases. This is called hyperplasia. At the second stage, called dysplasia, the new cancer cells look misshapen. The cancer cells then form a growing ball of cells, called a primary tumour. The tumour begins to push and squash the cells around it. As the tumour grows bigger, it burrows and invades into surrounding cells - this process is called invasion. When cancerous cells spread into a blood vessel or a lymph node, they can travel in the blood or lymph fluid to other parts of the body where they start to divide once again. This process is called metastasis, which means that the cancer has spread to other areas of the body.
Cancer causes more fear than any other disease. However, many cancers can now be treated and put into remission. This means traces of cancer are no longer found in the body following treatment. For example people with prostate, bladder, skin, uterine, or breast cancer have at least an 80% chance of being disease-free (without cancer) 5 years after being diagnosed with cancer, assuming the cancer was detected and treated at an early stage.
The exact cause of cancer is not known, but various factors are likely at play. Although genetic factors have been linked to certain types of cancers, less than 10% of cancers are inherited. Less than 10% of breast cancers are associated with mutated genes known as BRCA1 and BRCA2. These two inherited genes account for about 50% of the inherited forms of breast cancer.
Most forms of cancer are due to genetic mutations of cells that occur within a person's life as a result of environmental factors such as cigarette smoke or exposure to radiation. Exposure to the following environmental factors can cause cancer:
Cancer can cause many different types of symptoms depending on the type of cancer and what stage it's in. Cancer cells pressing on or invading surrounding cells can cause severe pain. Organs (like the liver or pancreas) that are being invaded by the cancer can't work properly. Some symptoms, called paraneoplastic syndromes, are caused not by the tumour itself but by chemicals or hormones produced by the tumour. The chemicals and hormones can cause an autoimmune reaction where the body produces antibodies against itself. They can also affect the normal functioning of organs or even kill healthy cells.
Some of the complications of cancer can be life-threatening. Cancer can cause fluid to fill the sacs surrounding the heart or lung, making it very hard to breathe. Cancer can also block the veins that return blood from the upper parts of the body to the heart. This causes the veins in the chest and neck to swell. Cancer can also press on the spinal cord or spinal cord nerves, causing pain or the loss of function of the nerve. The longer a nerve has been damaged, the less likely it will recover. Hypercalcemic (high calcium) syndrome occurs either when a cancer produces a hormone that dangerously raises the body's calcium levels or when cancer extensively invades the bones.