How cancer spreads
When cancer spreads from where it starts to another part of the body, it is called metastasis. Metastatic cancer may be treated differently than the primary cancer. Watch this video to learn more about how cancer spreads and how metastatic cancer can be treated.
The Cancer Basics video series is proudly sponsored by BMO.
Narrator: Understanding how cancer spreads helps doctors decide which treatments are likely to work best.
[A doctor in a lab coat appears. Next to her, a circle with pill bottles representing chemotherapy or hormone therapy appear. Then another circle with a gloved hand and scalpel appears to represent surgery. Finally a circle with a radiation machine appears. The scene ends.]
Narrator: Cancer begins in cells.
[A simple outline of a body appears. A single large yellow cell is in the middle of the chest.]
Narrator: Our bodies are made up of trillions of cells. Cells group together to form tissues and organs.
[As the narrator speaks, the single cell divides into many cells. Then the cells group together to form the lungs.]
Narrator: Genes inside the cells tell them what to do and when to grow, multiply and die.
[The outline of the body shifts to the right of the screen. A callout circle highlights a single cell in a lung. Another callout shows a double helix of DNA in the nucleus of the cell.]
Narrator: Sometimes genes can mutate, or change. When this happens, the genes stop sending the correct messages to cells. They don’t tell cells to stop multiplying or to die.
[The DNA changes so it becomes darker and uneven. When this happens, the cell also changes so it has an irregular shape and it turns blue.]
Narrator: These changed cells multiply and grow out of control.
[The callout with the DNA disappears and the focus shifts to the single mutated cell. This mutated cell then multiplies.]
Narrator: As more and more abnormal cells continue to multiply, they build up and form a tumour. This tumour is called the primary cancer.
[The callout with the mutated cells disappears and the scene zooms in on the lung. There are blue cancer cells grouped together in a tumour in the lung. The scene ends.]
Narrator: As a tumour grows, it can push on normal tissue around it and spread. Cancer cells can also break down normal cells and grow into, or invade, other tissue.
[A tumour made up of blue mutated cells sits on a membrane that separates different tissues in the body. A callout appears to show the individual cancer cells on one side of the membrane and healthy cells on the other. Some of the cancer cells move through the membrane. They push aside and replace some of the healthy cells. The scene ends.]
Narrator: Once the tumour grows into nearby tissue, cancer cells can move into the blood or lymphatic system.
[The doctor appears on the left side of the screen. On the right side, a simple outline of a body appears. It has veins and arteries that represent the blood. It also has the tonsils, adenoid, thymus and spleen, which represent the lymphatic system.]
Narrator: They can travel through the blood or lymph fluid to other areas of the body, such as lymph nodes, the bones, the brain, the liver or the lungs.
[As the narrator speaks, a blue cancer cell appears in the chest. More cancer cells appear to trace how cancer can travel through the blood from the chest to the brain. Then different callouts appear to show lymph nodes in the neck, the femur bone in the thigh, the brain in the head, the liver on the right side of the body and the lungs in the chest. The scene ends.]
Narrator: When cancer spreads from where it first started to another part of the body, it’s called metastatic cancer. For example, if cancer that started in a lung spreads to the brain, it is metastatic lung cancer, not brain cancer.
[A simple outline of a body appears. There is a blue circle in the chest to represent lung cancer. An arrow points from the circle in the chest to the head. A smaller blue circle appears in the head to represent that the lung cancer has spread to the brain. When the narrator talks about cancer that started in a lung, a circle with lungs appears next to the chest. When the narrator talks about the cancer spreading to the brain, a circle with a brain appears next to the head. The scene ends.]
Narrator: Doctors give cancer a stage based on the size of the tumour, where cancer is in the body and if it has spread.
[The doctor is sitting at a desk. On the monitor in front of her is an x-ray showing a tumour in a lung. As the narrator speaks, an outline of a body appears on the right of the screen. There is a blue circle in the chest to represent where cancer is in the body.]
Narrator: Knowing the stage helps doctors understand how cancer has grown or spread. This helps them plan your treatment.
[The outline of the body disappears and the scene zooms out to show a man with lung cancer and his partner sitting with the doctor in her office. Callouts appear next to the couple to represent radiation therapy and chemotherapy.]
Narrator: Metastatic cancer may have different treatment options and a different prognosis and survival rate than a primary cancer that hasn’t spread.
[As the narrator speaks, 2 more callouts appear, representing a different type of chemotherapy and surgery. The scene ends.]
Narrator: The goal of treatment is to destroy all the cancer cells in the body.
[The doctor appears on the right of the screen and an outline of a body appears on the left. A callout pointing to the chest of the body appears. In the callout circle is a sample of cells that shows a mix of healthy yellow cells and blue cancer cells. As the narrator speaks, all of the cancer cells except one disappear and several healthy cells fade.]
Narrator: But sometimes cancer cells are left behind. Even one cancer cell can grow and divide to become a new tumour. So it is normal to worry about cancer spreading or coming back.
[As the narrator speaks, more cancer cells appear in the callout with the sample of cells. Then the outline of the body becomes smaller and moves to the centre of the screen. The man with cancer appears on the left and the doctor is explaining to him that the cancer has come back. The scene ends.]
Narrator: This is why follow-up after treatment is an important part of cancer care. Your doctor will do tests to see if the cancer has spread or if it has come back in any part of the body. If cancer is found, it can be treated as soon as possible.
[The man with cancer appears on the left of the screen. A nurse has taken a sample of his blood. A vial of blood appears in a circle next to the nurse. Then a pathologist appears in the centre of the screen. She is examining the blood sample under a microscope. Finally the man with cancer appears on the right of the screen. He is sitting in a chair and receiving chemotherapy. The scene ends.]
Narrator: Follow-up visits also give you time to ask questions and talk to your doctor about the chances that cancer could spread.
[The doctor appears on the left of the screen and the man with cancer is on the right. Speech bubbles appear to show the man asking questions and the doctor answering them. Then the doctor hands him some pamphlets with more information. The scene ends.]
Narrator: The Canadian Cancer Society is also here to help. Visit cancer.ca or call 1-888-939-3333.
[The Canadian Cancer Society’s name, logo, phone number and website address appear in the centre of the screen. The Bank of Montreal (BMO) logo appears below as a proud sponsor of the Cancer Basics video series.]