anon-181898 on 18 Jun 2018.
Eóghan Forde answered on 18 Jun 2018:
Cancer cells can spread to other parts of the body through the bloodstream or lymphatic system. There they can start to grow into new tumours.
The lymphatic system is a system of thin tubes and lymph nodes that run throughout the body. These tubes are called lymph vessels or lymphatic vessels. The lymph system is an important part of our immune system. It plays a role in fighting bacteria and other infections as well as destroying old or abnormal cells, such as cancer cells.
Cancers are named according to where they first started developing. For example, if you have lung cancer that has spread to the bone, it will be called lung cancer with bone metastases or secondaries. It is not called bone cancer. This is because the cancerous cells in the bone are actually cancerous lung cells. They are not bone cells that have become cancerous.
In order to spread, some cells from the first cancer must break away, travel to another part of the body and start growing there. Cancer cells don’t stick together as well as normal cells do. They may also produce substances that stimulate them to move.
Spread through the blood circulation and lymphatic system:
When the cancer cells go into small blood vessels they can then get into the bloodstream. They are called circulating tumour cells (or CTCs). The circulating blood sweeps the cancer cells along until they get stuck somewhere. Usually, they get stuck in a very small blood vessel such as a capillary.
Then the cancer cell must move through the wall of the capillary and into the tissue of the organ close by. The cell can multiply to form a new tumour if the conditions are right for it to grow and it has the nutrients that it needs.
Spread through the lymphatic system:
Cancer cells can go into the small lymph vessels close to a primary tumour and travel into nearby lymph glands. In the lymph glands, the cancer cells may be destroyed but some may survive and grow to form tumours in one or more lymph nodes. Doctors call this lymph node spread.
I hope this helps!
Here is an interesting video explaining what I have just said:
Alex Haragan answered on 18 Jun 2018:
A good answer from Eoghan.
I will add that tumours can also spread in a few other ways. Bowel cancers can spread through a slightly unusual manner – parts of the cancer will break off and travel down the gut (using the same mechanisms that digested food does) and can end up spreading to bits of the bowel away from where it started.
Also slightly different, but cancers can be very aggressive and simply decide to grow into neighbouring tissues. Even though a cancer might be of, say, pancreatic origin, it might grow through the pancreas and straight into the surrounding tissues like the stomach, small bowel, gall bladder, liver.
Some types of cancer can also spread along nerves. This is called “Perineural” growth and has been known to occur in a variety of cancers like prostate, pancreas and bowel cancer. Nerves have a sheath or covering, and cancers can grow into and along these nerve bundles and into new areas.
Cancers are tricky things and you can see why!
On a related note there has been recent research activity in the study of cancer cells that spread but lay dormant. It is thought cancer cells could spread earlier in development than we assume, but lay dormant for months or even years – and explain the “relapse” of cancer seen years later even when it looks like it has all gone. Some researchers suggest we don’t even need to kill these cells – but just keep them dormant.