Cancer is a disease of the cells in the body. There are many different types of cell in the body, and many different types of cancer which arise from different types of cell. What all types of cancer have in common is that the cancer cells are abnormal and multiply out of control. However, there are often great differences between different types of cancer. For example:
- Some grow and spread more quickly than others.
- Some are more easy to treat than others, particularly if diagnosed at an early stage.
- Some respond much better than others to chemotherapy, radiotherapy, or other treatments.
- Some have a better outlook (prognosis) than others. For some types of cancer there is a very good chance of being cured. For some types of cancer, the outlook is poor.
So, cancer is not just one condition. In each case it is important to know exactly what type of cancer has developed, how large it has become, whether it has spread, and how well the particular type of cancer responds to various treatments. This will enable you to get reliable information on treatment options and outlook.
Cancer is the general name for a group of more than 100 diseases. Although there are many kinds of cancer, all cancers start because abnormal cells grow out of control. Untreated cancers can cause serious illness and death.
Normal cells in the body
The body is made up of trillions of living cells. Normal body cells grow, divide to make new cells, and die in an orderly way. During the early years of a person’s life, normal cells divide faster to allow the person to grow. After the person becomes an adult, most cells divide only to replace worn-out or dying cells or to repair injuries.
How cancer starts
Cancer starts when cells in a part of the body start to grow out of control. Cancer cell growth is different from normal cell growth. Instead of dying, cancer cells continue to grow and form new, abnormal cells. Cancer cells can also invade (grow into) other tissues, something that normal cells can’t do. Growing out of control and invading other tissues are what makes a cell a cancer cell.
Cells become cancer cells because of DNA (deoxyribonucleic acid) damage. DNA is in every cell and it directs all its actions. In a normal cell, when DNA is damaged the cell either repairs the damage or dies. In cancer cells, the damaged DNA is not repaired, but the cell doesn’t die like it should. Instead, the cell goes on making new cells that the body doesn’t need. These new cells all have the same damaged DNA as the first abnormal cell does.
People can inherit abnormal DNA (it’s passed on from their parents), but most often DNA damage is caused by mistakes that happen while the normal cell is reproducing or by something in the environment. Sometimes the cause of the DNA
damage may be something obvious like cigarette smoking or sun exposure. But it’s rare to know exactly what caused any one person’s cancer.
Oldest descriptions of cancer
Human beings and other animals have had cancer throughout recorded history. So it’s no surprise that from the dawn of history people have written about cancer. Some of the earliest evidence of cancer is found among fossilized bone tumors, human mummies in ancient Egypt, and ancient manuscripts. Growths suggestive of the bone cancer called osteosarcoma have been seen in mummies. Bony skull destruction as seen in cancer of the head and neck has been found, too.
Our oldest description of cancer (although the word cancer was not used) was discovered in Egypt and dates back to about 3000 BC. It’s called the Edwin Smith Papyrus and is a copy of part of an ancient Egyptian textbook on trauma surgery. It describes 8 cases of tumors or ulcers of the breast that were removed by cauterization with a tool called the fire drill. The writing says about the disease, “There is no treatment.”
The origin of the word cancer is credited to the Greek physician Hippocrates (460-370 BC), who is considered the “Father of Medicine.” Hippocrates used the terms carcinos and carcinoma to describe non-ulcer forming and ulcer-forming tumors. In Greek, these words refer to a crab, most likely applied to the disease because the finger-like spreading projections from a cancer called to mind the shape of a crab. The Roman physician, Celsus (28-50 BC), later translated the Greek term into cancer, the Latin word for crab. Galen (130-200 AD), another Greek physician, used the word oncos (Greek for swelling) to describe tumors. Although the crab analogy of Hippocrates and Celsus is still used to describe malignant tumors, Galen’s term is now used as a part of the name for cancer specialists - oncologists.
In most cases, the cancer cells form a tumor. Over time, the tumors can replace normal tissue, crowd it, or push it aside. Some cancers, like leukemia, rarely form tumors. Instead, these cancer cells involve the blood and blood-forming organs and circulate through other tissues where they grow.
How cancer spreads
Cancer cells often travel to other parts of the body where they can grow and form new tumors. This happens when the cancer cells get into the body’s bloodstream or lymph vessels. The process of cancer spreading is called metastasis.
No matter where a cancer may spread, it’s always named based on the place where it started. For example, colon cancer that has spread to the liver is called metastatic colon cancer, not liver cancer. In this case, cancer cells taken from the liver would be the same as those in the colon. They would be treated in the same ways too.
Local growth and damage to nearby tissues
Malignant cells multiply quickly. However, to get larger, a tumour has to develop a blood supply to obtain oxygen and nourishment for the new and dividing cells. In fact, a tumour would not grow bigger than the size of a pinhead if it did not also develop a blood supply. Cancer cells make chemicals that stimulate tiny blood vessels to grow around them which branch off from the existing blood vessels. This ability for cancer cells to stimulate blood vessels to grow is called angiogenesis. Malignant cells have the ability to push through or between normal cells. So, as they divide and multiply, malignant cells invade and damage the local surrounding tissue.
Spread to lymph channels and lymph nodes
Some malignant cells may get into local lymph channels. (The body contains a network of lymph channels which drains the fluid called lymph which bathes and surrounds the body’s cells.) The lymph channels drain lymph into lymph glands (called lymph nodes). There are many lymph nodes all over the body. A malignant cell may be carried to a lymph node and there it may become trapped. However, it may multiply and develop into a tumour. This is why lymph nodes that are near to a tumour may enlarge and contain cancerous cells.
Spread to other areas of the body
Some malignant cells may get into a local small blood vessel (capillary). They may then get carried in the bloodstream to other parts of the body. The cells may then multiply to form secondary tumours (metastases) in one or more parts of the body. These secondary tumours may then grow, invade and damage nearby tissues, and spread again.
Why do non-cancerous (benign) tumours not spread to other areas?
Cells that make up benign tumours are different to cancerous (malignant) cells. Cells in benign tumours tend to be quite similar to normal cells. They do not invade local tissues. A benign tumour often grows slowly within a capsule or within normal cells which surround the tumour. A benign tumour tends to look and feel smooth and regular and have a well-defined edge. This is unlike a malignant tumour which may look craggy and irregular, and its edges tend to be mixed up with the nearby normal cells and tissue.
What is carcinoma in situ?
A carcinoma in situ is the very early stage of a cancer when the abnormal cancer cells are confined to their original site. At this stage no tumour has grown and no cancer cells have spread. It may be that many cancers remain at this dormant stage for months, or even years, before they start to grow and spread into a proper cancer. This may be because the cells of the carcinoma in situ do not have the ability to stimulate new blood vessels (see above under ‘Local growth and damage to nearby tissues’ - angiogenesis). If they cannot stimulate new blood vessels to grow then the cancer itself cannot grow or spread.
It is thought that one or more of the cells in a carcinoma in situ may then mutate after some time (some genes may be altered). This then gives them the ability to make chemicals to stimulate new blood vessels. The cancer then grows and spreads as described above.
A carcinoma in situ contains only a small number of cells and is usually too small to be detected by scans or X-rays. However, some screening tests may detect a carcinoma in situ. For example, some cells from an abnormal cervical screening test, looked at under the microscope, may show carcinoma in situ. These cells can then be destroyed by treatment which prevents cancer from developing. Sometimes a small sample (a biopsy) taken from a part of the body may show a carcinoma in situ.
How cancers differ
Different types of cancer can behave very differently. For instance, lung cancer and skin cancer are very different diseases. They grow at different rates and respond to different treatments. This is why people with cancer need treatment that’s aimed at their kind of cancer.
Tumors that are not cancer
A tumor is an abnormal lump or collection of cells, but not all tumors are cancer. Tumors that aren’t cancer are called benign. Benign tumors can cause problems - they can grow very large and press on healthy organs and tissues. But they can’t grow into (invade) other tissues. Because they can’t invade, they also can’t spread to other parts of the body (metastasize). These tumors are seldom life threatening.
What are the most common forms of cancer?
Cancer can occur anywhere in the body. In women, breast cancer is most common. In men, it’s prostate cancer. Lung cancer and colorectal cancer affect both men and women in high numbers.
There are five main categories of cancer:
- Carcinomas begin in the skin or tissues that line the internal organs.
- Sarcomas develop in the bone, cartilage, fat, muscle or other connective tissues.
- Leukemia begins in the blood and bone marrow.
- Lymphomas start in the immune system.
- Central nervous system cancers develop in the brain and spinal cord.
How is cancer treated?
Treatment options depend on the type of cancer, its stage, if the cancer has spread and your general health. The goal of treatment is to kill as many cancerous cells while minimizing damage to normal cells nearby. Advances in technology make this possible.
The three main treatments are:
Surgery: directly removing the tumor
Chemotherapy: using chemicals to kill cancer cells
Radiation therapy: using X-rays to kill cancer cells
The same cancer type in one individual is very different from that cancer in another individual. Within a single type of cancer, such as breast cancer, researchers are discovering subtypes that each requires a different treatment approach.
The University of Texas MD Anderson Cancer Center