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About Cancer

Reviewed June 2020

What is cancer?

Cancer starts when the cells of an organ or tissue in the body become abnormal. They grow and multiply out of control. Normal cells have a life cycle. They reproduce themselves throughout the body to replace worn out tissue, to heal wounds and to maintain healthy organs. When something happens and cells grow out of control they usually form a mass, called a tumour.  

Some tumours grow only at the site where they begin (locally). These are called benign tumours. Other tumours grow locally but they might also invade and destroy the normal tissue around them or they might spread to distant parts of the body. These tumours are called malignant tumours or cancers. 

Sometimes malignant cells break loose from the original (primary) tumour, get carried to other parts of the body and start growing in the new site as an independent secondary cancer. A tumour that has spread in this way has ‘metastasized’ and the secondary tumour (or tumours) is called a metastasis (or metastases).

What causes cancer?

Most cancers occur by chance (randomly) in people over the age of 50 as the result of damage to their genes. Genes play a role in all cancers. Many genes in the human body help to control how the cells divide and grow. When changes (called mutations) occur in those genes, they may lose that control over the cells. Because most cancers do not happen until a cell is affected by several gene mutations, most cancers are not seen until later in life. Gene mutations may be caused by aging, exposure to chemicals, radiation, hormones or other factors within the body and the environment. Over time, a number of gene mutations may occur in a cell, allowing it to divide and grow in a way that becomes a cancer. 

Metastasis: how cancer spreads

Tumours are called malignant because they have the ability to invade normal tissues (replacing healthy cells with cancer cells) and to metastasize (spread) to other parts of the body. Often, cancer deaths don’t come from the primary site where the cancer first began, but from the metastases. For example, a patient with stomach cancer may actually die from liver failure after the cancer has spread to the liver. 

When one type of cancer spreads to another part of the body, it doesn’t become another type of cancer. For example, if a person with colon cancer develops a metastasis in the lung, then the tumour growing in the lung has the same features as the colon cancer. It is the same cancer in a new place. This is why it is very important for the doctors treating a patient to be able to find the primary site where the cancer started. 

Metastasis takes place in many ways: through the lymphatic system, through the blood, by spreading through body spaces such as the abdominal cavity, or through implantation. Cancers can spread by more than one route.

Lymphatic system

The most common way for cancer to spread is through the lymphatic system. The lymph system has its own channels that circulate throughout the body, similar to the veins and arteries of the bloodstream. These channels are very small and carry fluid called lymph throughout the body.

Often when a solid tumour is removed by surgery, the surgeon will remove not only the tumour but the neighboring lymph glands, even though there is no visible sign of cancer in those glands. This is done as a precautionary measure, because if even one cell has broken away from the tumour and lodged in the lymphatic system, the cancer could continue growing and metastasizing.

Circulatory system

Cancer can metastasize through the blood. All cells (healthy and cancer) must have a blood supply in order to live, so all cancer cells have access to the bloodstream. Malignant cells can break off from the tumour and travel through the bloodstream until they find a suitable place to start growing a new tumour. Tumours that spread by blood almost always metastasize through the veins rather than through the arteries. Sarcomas spread through the bloodstream, as do certain types of carcinomas, like carcinoma of the kidneys, testicular carcinoma, and Wilms' tumour, a type of kidney cancer seen in young children.

Local invasion

Cancers can spread by local invasion -- by growing into the healthy tissue that surrounds the tumour. Some cancers that spread this way do not travel very far from the original site. An example of this kind of cancer is basal cell carcinoma of the skin. When this kind of cancer is removed by surgeon, a wide area of healthy tissue surrounding it is also removed and it is usually "cured" immediately. Unless some cells have been left behind, it is very unlikely that it will recur. However, it is possible that a second cancer of the same kind may start to grow at a later time at a completely different site -- the new growth would not be connected with the first.


A very rare type of metastasis is caused by implantation or inoculation. This can happen when a biopsy is done or when cancer surgery is performed. Malignant cells may accidentally drip from a needle or an instrument (this is also called a "spill"). That is why, if the cancer is small enough, the surgeon tries to avoid spills by removing it completely at the initial surgery (at the time of the biopsy).

Cancers do not spread in a completely random fashion. Some parts of the body accept metastases more easily than others. For example, cancers rarely metastasize to the skin, but they often metastasize to the liver and lungs. Each type of cancer has its own pattern for metastases. See the individual cancer pages for more information.

Can cancer be prevented? 

Experts estimate that around 4 in 10 cancer cases could be prevented through lifestyle changes (modifiable risk factors). What you eat, whether you smoke, your level of physical activity, and how much you protect yourself from the sun are all lifestyle choices that can affect your chances of getting cancer, and your chances of preventing it. Alcohol consumption also plays a part in some cancers. For more details, please visit our prevention pages

There is information about healthy living after cancer in our Life After Cancer section.

The American Institute for Cancer Research has conducted extensive reviews of cancer prevention research on food, nutrition and physical activity. They have published recommendations to lower people's risk of getting cancer and they advise following the same evidence-based guidelines after cancer treatment. 

Many of the things you can do to lower your risk of cancer will also reduce your risk of developing other serious chronic diseases. For general healthy living and disease prevention advice, visit the Provincial Health Services Authority's Staying Healthy pages.

Hereditary cancer 

Most cancers are not caused by an inherited (hereditary) risk. For information about hereditary or inherited risk, see our Hereditary Cancer Program information.

Types of cancer

Cancers are usually named after the part of the body where the cancer first began. The name does not change even if the cancer spreads to another part of the body.

For example, if breast cancer spreads (metastasizes) to the lung, it is called breast cancer with lung metastases. If chemotherapy is indicated as the best treatment, breast cancer drugs would be used to treat the lung metastases. Other cancers such as leukemia (a cancer involving the blood) may not mention a tumour site in the name.

Different types of cancer vary in their signs and symptoms, how fast they grow, how they spread, and how they react to different treatments. This is why it is important to accurately diagnose a cancer, so that treatment begins as soon as possible.

Treatment options

Surgery, cancer drugs and radiation therapy are all proven to cure cancer, extend life, or improve quality of life.

The type of treatment or the order of treatment will be different for individual patients, depending on the location of the tumour, the stage of the disease at diagnosis and what BC Cancer treatment guidelines indicate.

For example, surgery is not always the first treatment. Sometimes radiation therapy or cancer drugs are used to shrink the tumour before surgery, or chemotherapy may be the best first option. Sometimes one type of treatment is used, usually a combination of treatments are used. 

Cancer drugs are often given in combinations called chemotherapy protocols. Patient handouts for some of these protocols are available in the BC Cancer Health Professionals section. Your healthcare team will discuss your specific treatment strategy with you in detail.

Patients and families may hear the term "investigational treatment". This means that the treatment is being studied in a clinical trial to determine whether it is a safe and effective way to treat cancer.

"Support programs", "alternative" or "complementary" are also terms patients may come across. It is important to understand there are critical differences between conventional treatments, support (coping with cancer) programs and complementary and alternative therapies.

Conventional therapies have been proven to cure cancers. Support programs are used to help patients who are using conventional treatments. Alternative or complementary therapies have not usually undergone rigorous scientific testing to see if they are safe or effective.

Our Coping with Cancer section has information on nutrition, emotional, financial and practical support, how to deal with symptoms and side effects, and information about palliative care.

BC Cancer provides cancer care and treatment through a unique system of provincial programs, including teams of health-care professionals (scientists, physicians, nurses, pathologists, radiologists, pharmacists, nutritionists and counsellors) who research and develop treatment policies and guidelines for specific types of cancer. 

These guidelines are based on solid, scientific evidence and are used by health-care professionals throughout the province.

This ensures that all British Columbians have access to the same, reliable, high-quality care.

Surgery is often the first step in cancer treatment because it can be used to both diagnose and/or treat cancer. More than half of the people diagnosed with cancer will have some type of surgery or operation at some point. To find out if surgery may be considered to diagnose or treat a specific cancer please review the appropriate Types of Cancer page.

Surgery can be used to remove tumours confined to a small space. Surgery can also be used to reduce the size of large tumours so that follow-up treatment by radiation therapy or chemotherapy will be even more effective.

Surgery alone sometimes cures cancer. Sometimes it is used in conjunction with other treatments such as chemotherapy (cancer drugs) or radiation therapy.

In addition to curing cancer, surgery can also be used as a preventive measure by removing pre-cancerous conditions. Surgery may also be recommended as a palliative method to help reduce pain or other symptoms.

Some cancer surgeries are performed at the BC Cancer, Vancouver Site; however, many more are performed by surgeons at hospitals throughout the province. Surgical oncologists are specialized in using surgery to treat cancer. 

BC Cancer coordinates the BC Surgical Oncology Network, with the aim of promoting quality cancer surgery across the province. The BCSON sets standards for cancer surgeries and provides training and continuing medical education for surgeons.

Our Coping with Cancer section has information on nutrition, emotional, financial and practical support, how to deal with symptoms and side effects, and information about palliative care.


This page provides general information on drug therapies for cancer and what they can do. For information on specific cancer drugs, see our Cancer Drug Manual.


Cancer drugs such as chemotherapy, hormone therapy, and other biological or genetic treatments, are used to destroy cancer cells. Sometimes the goal of cancer drugs is to cure. When cure is not possible, cancer drugs can often prolong life or improve quality of life.

Drugs can work in a number of ways to kill cancer cells.

  • Chemotherapy drugs (cytotoxic) can slow down cancer cells from growing or multiplying. They can also encourage these cells to die naturally (apoptosis). In general, chemotherapy drugs can harm some of the healthy cells in the same way, causing side effects.
  • Hormone drugs usually stop your body’s hormones from helping some cancers to continue to grow.
  • Biological therapy involves drugs which help the immune system in your body to fight against cancer.
  • Targeted drug therapy includes drugs which are designed to attack only certain areas found mainly in cancer cells. These drugs tend to cause less harm to healthy cells, which means fewer side effects.

Chemotherapy uses drugs to treat cancers of the blood and bone marrow as well as for cancers of the lymphatic system (lymphomas). Chemotherapy is also used to treat cancer when it has spread, when it has come back, or when there is a strong chance it could come back (recur). Hormone therapy uses drugs to interfere with hormone production or hormone action, to kill cancer cells or slow their growth. Surgery is also used to remove hormone-producing glands to slow or kill cancer cells.

Cancer drugs can:

  • Cure specific types of cancer.
  • Shrink tumours prior to surgery or radiation therapy.
  • Prevent cancers from spreading.
  • Control the spread of cancer when a tumour cannot be completely removed by surgery or radiation therapy.
  • Relieve symptoms such as pain.
  • Stop or slow tumour growth.

If you would like assistance dealing with side effects from cancer drugs please go to Managing Symptoms and Side Effects.

Why do some patients receive cancer drugs and others don't?

Chemotherapy is recommended to patients as an option based on the following:

  • Does the specific cancer react to chemotherapy? Only certain types of cancers (the ones with large proportions of dividing cells) are responsive to drugs. These are usually small tumours (either because they are detected early or because most of the tumour has been removed by surgery or radiation) or are systemic cancers like leukemias and lymphomas (systemic means they are everywhere in the body)
  • Location of the Tumour: Even if the tumour can respond to cancer drugs, its actual location will affect the choice of treatment. In some cases, tumour location will make cancer drugs, perhaps combined with radiation therapy, the only treatment option. For example, certain brain tumours cannot be removed surgically, so cancer drugs and/or radiation therapy are the only choices
  • General Condition of the Patient: Your body has to be otherwise healthy in order to tolerate some chemotherapy drugs. Cancer patients are often shocked when they hear medical personnel refer to them as healthy. How can someone with cancer be healthy? When doctors term a cancer patient "healthy", they are referring to how well the body is functioning, except for the site of the cancer. When they speak about a cancer patient being "sick" they are talking about a serious breakdown in the functioning of vital organs and systems

Selecting Specific Drugs

For some situations, only one drug is needed for effective chemotherapy. For others, a combination of drugs is used. The specific drug plan is called a Chemotherapy Protocol.

The selection of drug combinations depends on three things:

  • The proven effectiveness of each drug when used alone against that cancer.
  • A difference in each drug's method of attacking the cancer (so that maximum cancer-kill can be achieved in each cycle while minimizing the chance of developing resistance to any one drug).
  • A difference in the side effects of each drug (minimally overlapping toxicity), so that your healthy tissue will not be badly damaged by the cancer drugs.

How are cancer drugs given?

How often you receive drugs depends on your:

  • Treatment program (which may be called a regime, regimen, or protocol)
  • Cycle length: how long your cycle is (from the start of one round of chemotherapy to the start of another)
  • Number of cycles: how many cycles are in your treatment plan. Typical cycles are two to six weeks long. The cycle is divided into two parts: the period when you receive the drugs and the period of rest and recovery before the next cycle


Intravenous (IV) drugs are injected directly into a vein. This is done either in the form of a fluid drip (commonly called an "IV" or "drip") or as an IV push. If it's given as a drip, a needle is inserted into your vein. The needle is connected to a tube that's attached to a bag or bottle of the drug that is hanging on a pole. The drug drips into the vein at a specified rate. An "IV push" is like a regular shot (the drug is in a syringe rather than a bag), but goes directly into a vein.

IV chemotherapy can take from 15 minutes to 12 hours or longer.

If a vein is not easily accessible, a temporary port can be surgically implanted under the skin in the chest or in an arm or leg. The port allows direct access to a vein for the duration of your chemotherapy treatments. The port can remain in place for several years. One or more small scars will result from the placement of this port.

Other Injections

  • Intramuscular (IM) - a regular shot into the muscle of the arm, thigh, or buttocks
  • Subcutaneous (SQ) - a shot under the skin
  • Intra-Arterial (IA) - the same as an IV (drip or push) except that the needle is inserted into an artery instead of a vein
  • Intrathecal (IT) - injecting the drug directly into the spinal fluid that circulates over the brain and spinal cord. Sometimes a device is implanted under the skin on top of the head to make access easier
  • Intracavitary (IC) 0 injecting drugs directly into a cavity, or "empty space," usually around the lung (pleural space) or into the abdomen
  • Regional Perfusion - a technique that concentrates certain drugs in one area (usually arms or legs) by creating a closed-circuit system in the bloodstream. A tourniquet is used to stop the blood flow out of the affected area so that no harm comes to other organs. The drug is put into the artery, which carries it to the cancerous area; it is then taken out of a vein and pumped back into the artery for a continuous high concentration of the drug.


You swallow the drugs either in the form of pills, capsules or liquid.


For some cancers, usually skin cancers, drugs can be administered in the form of a cream you use on your skin.

Side Effects

Managing Symptoms and Side Effects will help you cope with some of the adverse effects of treatment.


Read about radiation therapy
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