radiotherapy centre - doctor and testicular cancer patient

How Does Cancer Spread To Other Parts Of The Human Body?

A course of radiotherapy is undertaken through extensive, cautious planning to ensure that it has the greatest effect possible to relieve pain, prolong life and improve the quality of everyday existence.

When someone enters a radiotherapy centre to undergo consultation and treatment, each case will have some unique elements to it, and whilst treatments such as stereotactic radiosurgery are focused predominantly on removing tumours and lesions based in the brain, this does not mean they necessarily originated there.

Cancers can spread in a process known as metastasis from one part of the body to the next, and understanding how this process works is important for understanding its implications on treatment.

Primary And Secondary Cancers

Oncologists will make an important distinction between a type of cancer and where it currently is in the body, which is important to avoid confusion when discussing a person’s condition.

For example, if someone has breast cancer that spreads to the brain, it will still be called breast cancer even though it is not located in the breast. The cells in the brain that are cancerous are breast cancer cells, not brain cancer ones

This concept is known as primary and secondary cancer. A primary cancer is one that originates in the place where the tumours are found, whilst a secondary cancer is where that cancer has spread elsewhere.

This is an important distinction to make because there are many different types of cancer, each of which has different methods of diagnosis, treatment and prevention that need to be used to manage it effectively, particularly when it comes to medication and chemotherapy used alongside radiotherapy.

Generally, a secondary cancer of the brain is found by examining an existing primary cancer, but there are times when the primary cancer no longer exists in the body, either by being removed or destroyed by past treatment, or being too small to be easily detected.

Whilst there are cases where oncologists can determine the type of cancer from the types of cells that comprise them, there are some cases where doctors cannot completely verify the original location or doing so would require intense tests that may not change the planned treatment. 

These are known as cancers of unknown primary and happen either due to a small primary cancer, a primary cancer that has already been destroyed by the immune system, or complexities with treatment that mean that certain tests cannot be used.

How Cancer Spreads

Cancer spreads through the body through either the blood or lymphatic system, which regulates and filters other bodily fluids.

A primary cancer growth spreads largely by breaking apart. Cancer growths are often unstable, and cells can break away or be stimulated to travel elsewhere.

From there, they find a way into the bloodstream, where they are swept along by the blood or other fluid until they get stuck in a tiny capillary. The cell then moves through the wall of the blood vessel and enters nearby organ tissue. 

If they have the right nutrients and conditions to grow, the cancer cells will form a tumour in the new location.

This is a very difficult process and whilst a lot of cancer cells will break off and enter the bloodstream, few will complete the process of forming a secondary cancer.

The blood flow itself can be powerful enough to destroy cells, whilst white blood cells in the blood can kill some of the cancer cells it finds.

Alternatively, cancer cells can spread through lymph vessels close to the primary tumour. This allows them to flow into lymph glands designed to drain damaged cells and excess bodily fluids.

If they survive this process, they can sometimes form tumours in a lymph node, and a swollen lymph node can sometimes be a marker for cancer, although lymph nodes can also swell due to the effects of infection.

Can Any Cancer Spread To The Brain?

Theoretically, any cancer can have a secondary growth in the brain, although some cancers are more likely to than others due to how relatively common they are.

These include:

  • Breast cancer.
  • Lung cancer.
  • Bowel cancer.
  • Kidney cancer.
  • Melanoma (a type of skin cancer).

Because these are common cancers, and their effects are well-known, secondary brain cancer can often be treated, particularly if it is found quickly.

Radiation therapies such as Gamma knife work as well for secondary brain cancer as they do for primary ones, and they can be used in combination with targeted drugs, chemotherapy and surgery to relieve pain and long-term effects.