There are over 100 different types of cancer. The disease can affect almost any organ in the body. The most common cancers found in North America are lung cancer, breast cancer and prostate cancer.
There are 6 main categories of cancer:
- carcinomas are tumors that start in the outer or inner lining of internal organs (called epithelial tissue ) and on the outer surface of the body;
- leukemias are cancers of the building blocks of the blood;
- lymphomas are the tumors that form in the lymphatic system;
- melanomas are cancers that start in cells that give pigmentation to the skin;
- sarcomas are tumors that start in connective tissue, such as muscles, bones, and cartilage
- mixed types of cancer having the characteristics of more than one cancer category.
In order for our body to grow, some cells divide and multiply to create new tissue, while other cells (such as muscles or nerves) do not divide or multiply. Our bodies have specific genes, called oncogenes , that govern the ability of cells to divide and grow. In addition, genes called tumor suppressor genes help prevent or repair genetic mutations that can cause cancer. . Cancer can occur when oncogenes are “turned on” at an inappropriate time, or tumor suppressor genes are turned off when they should be working. This results in excessive growth which takes the form of tumors.
Cancer cells go through different stages as they divide and multiply to form a tumor. At first, normal cells divide faster than they should and the total number of cells increases. This is called hyperplasia . In the second stage, called dysplasia , new cancer cells become deformed. They then form a growing cluster of cells, called a primary tumor . The tumor begins to grow and crush neighboring cells. As it grows, it widens its way and invades neighboring cells – this process is called invasion.. When cancer cells reach a blood vessel or a lymph node, they can pass through the bloodstream or lymph fluid to other parts of the body where they start dividing again. This process is called metastasis , which means that the cancer has spread to other areas of the body.
More than any other disease, cancer is scary. However, today many cancers can be treated and put into remission. This means that the treatment removes all traces of cancer in the body. For example, people with prostate, thyroid, skin, uterine, or breast cancer may have at least an 80% chance of living cancer-free 5 years after diagnosis, provided the cancer is detected and treated from its inception.
The exact cause of cancer is not known, but different factors can play a role in this process. Although genetic factors have been associated with some forms of cancer, less than 5% of cancers are associated with inherited genetic mutations. For example, BRCA1 and BRCA2 are two genes that have been shown to be associated with cancer, but less than 5% of breast cancers are associated with these genes.
Most forms of cancer are caused by genetic mutations in cells that occur during a person’s lifetime, under the influence of environmental factors such as smoking or exposure to radiation.
The following are the environmental factors that can cause cancer:
- ionizing radiation – the link between ionizing radiation and cancer has already been established, but it is not known how much radiation could increase the risk of cancer;
- sun rays – prolonged exposure (eg tanning) causes skin damage and may lead to skin cancer;
- chemicals – exposure to industrial dyes, asbestos and benzene is associated with cancer;
- smoking – smoking causes lung cancer; it is also associated with a greater risk of cancer of the mouth, larynx, esophagus, bladder and cervix;
- a virus – some viruses, such as the human immunodeficiency virus (HIV, which causes AIDS), are associated with an increased risk of liver cancer, lymphomas and sarcomas. The human papillomavirus (HPV, which causes condylomata acuminata) is associated with an increased risk of cancer of the mouth, anus and cervix.
Cancer can cause many different symptoms, depending on the type of cancer and the stage of the disease. Cancer cells that crush or invade neighboring cells can cause severe pain. Organs (such as the liver or pancreas) that are invaded by cancer can no longer function properly. Some symptoms, referred to as paraneoplastic syndromes , are not caused by the tumor itself but rather by the chemicals or hormones it secretes. These chemicals and hormones can cause an autoimmune reaction, where the body produces antibodies to fight against itself. It can also interfere with normal organ function or kill healthy cells.
Some cancer complications can be life threatening. For example, because of cancer, the membranes around the heart or lungs can become flooded with fluid, making it very difficult to breathe. Cancer can also block the veins that return blood from higher organs to the heart. This causes swelling of the veins in the chest and neck. Cancer can also put pressure on the spine or its related nerves, causing pain or loss of nerve function. The longer the injury lasts, the less chance there is of recovering the function of a damaged nerve. Hypercalcemic syndrome (elevated calcium levels) occurs when cancer produces a hormone that dangerously increases calcium levels in the body or when cancer invades the bones significantly.
To make the diagnosis, cancer specialists or oncologists should assess symptoms, perform a physical exam, and order blood tests and x-rays. The only way to know for sure whether the cells are cancerous is to take a sample of the tissue that contains these cells, a process called a biopsy . Laboratory staff then examine the cells under a microscope, and the information obtained from the biopsy allows the doctor to tell what type and stage of cancer is.
At the time of diagnosis, determining the stage of the cancer helps define the prognosis and the type of treatment a patient will receive. Doctors simply use a cancer classification system called the TNM system, which describes the size of the tumor and how far it has spread in the body. The choice of treatment depends largely on the stage of the cancer.
We can prevent certain types of cancer by making lifestyle changes: this is what is meant by primary cancer prevention. Cancers related to tobacco use (eg lung cancer) account for almost a third of all forms of fatal cancer. Therefore, quitting smoking would be an essential step in preventing cancers of the mouth, throat, esophagus and lung. By avoiding exposure to the sun and limiting the duration of exposure as well as using adequate protection (lotions with SPF and sunscreen) when in the sun, you can reduce the risk of skin cancer. . Diet is another important factor in cancer prevention: a diet high in fat is associated with a higher risk of certain cancers (such as breast cancer and prostate cancer), while
To treat cancer, we use surgery, radiation therapy, chemotherapy and, for some forms of cancer, hormones or drugs that block hormone secretion.
Surgery removes cancer cells that are clumped together. Many cancers are treated with surgery. Surgeons also remove normal cells surrounding cancer cells or the tumor, to determine whether or not the cancer has spread. When the cancer has already spread, it is very difficult to remove the cancer cells with surgery.
Radiotherapy is used to treat localized cancers. Radiation therapy can take different forms. A beam of radiation can be directed at the skin near the site of the cancer. Radiation kills cancer cells, but unfortunately it also destroys healthy cells. Newly designed devices allow radiation to be better focused on cancer cells and avoid healthy cells.. These particles adhere to cancer cells but not to normal ones. It also happens that radioactive particles are introduced into an organ near the cancer, transmitting a dose of radiation to cancer cells.
In chemotherapy, anti-cancer drugs are used. It is frequently used when the cancer has spread to several areas of the body. For many cancers, a combination of drugs is used because the results are better than with just one drug. We talk about a complete response to chemotherapy when no trace of cancer can be detected. However, some cancer cells can remain in the body undetected. Therefore, the cancer may come back after a period of remission. In a partial response, the size of the cancer decreases by more than 30%. Unfortunately, many cancers become resistant to cancer drugs. Some cancers (such as breast cancer) respond to hormonal actions, and hormones or drugs that block the hormonal action can be used to slow cancer growth.
Nowadays, genetic engineering makes it possible to intervene at the level of the genes which start or slow down cancerous growth and to regulate the enzymes which maintain the division and the growth of cancerous cells. Research continues to improve our tools to fight cancer, and some of the most promising avenues include cancer vaccines, antibodies combined with poisons, and chemicals that can cut off the blood supply to cancer.