Metastasis: How Does Cancer Spread?


The place in the body where cancer starts, or originates from, is called the primary cancer, or primary site. A very common and major concern when a patient is diagnosed with cancer is whether or not the cancer has spread to another area of the body.  If cancer spreads to a different part of the body it is referred to as a secondary cancer, or metastasis.[1] As such, the term metastasis refers to the development of secondary malignant growths at a distance from a primary site of cancer, or the process by which cancer develops in a different area of the body than where the cancer was first detected. 

Knowing how cancer can spread, as well as where it tends to spread to, is important and empowering. By educating oneself on metastasis, you can become more aware of how cancer works, and thus be more active in facing cancer head-on. 


Metastasis, or the process by which cancer spreads, can occur through multiple processes. For example, cancer can move locally when its cells spread into nearby normal tissue. However, “cancer can also spread regionally, to nearby lymph nodes, tissues, or organs. And it can spread to distant parts of the body. When this happens, it is called metastatic cancer. For many types of cancer, it is also called stage IV (four) cancer.”[2]

Cancer cells can spread through the body in a series of steps. These steps may include:

  1. Growing into, or invading, nearby normal tissue

  2. Moving through the walls of nearby lymph nodes or blood vessels

  3. Traveling through the lymphatic system and bloodstream to other parts of the body

  4. Stopping in small blood vessels at a distant location, invading the blood vessel walls, and moving into the surrounding tissue

  5. Growing in this tissue until a tiny tumor forms

  6. Causing new blood vessels to grow, which creates a blood supply that allows the tumor to continue growing

 It is important to note that, “Metastatic cancer has the same name as the primary cancer. For example, breast cancer that spreads to the lung is called metastatic breast cancer, not lung cancer. It is treated as stage IV breast cancer, not as lung cancer.”


What happens if cancer spreads, but it is too small to be identified positively? This can happen, and it is commonly referred to as micrometastasis. While blood tests cannot definitively say if cancer has spread, they fortunately can reveal “certain proteins released by the cancer cells,” thus notifying if there are metastases in the body too small to show up on a scan. Micro-metastases are by definition smaller than regular than metastases, and thus, may be easier to treat. The goal is to “kill any areas of cancer cells before they grow big enough to be seen on a scan,” so your doctor may prescribe additional or concurrent treatments directed towards the micro-metastases.

In Summary

While metastasis can be unpleasant to learn about, scientists and researchers are making advancements on cancer and how it spreads all the time. For example, in August of 2016, a research team from Goethe University, Frankfurt, and the Max Planck Institute of Germany published that they have discovered how metastases push “through the walls of the small blood vessels by targeting a molecule known as Death Receptor 6 (no, really, that’s what it’s called).” It then sets off a process in the blood vessels which allow cancer to spread.[3] This scientific finding is incredible and an amazing step forward for the cancer research society because now that we know how it spreads, we are more likely to now learn how to stop such processes from occurring, this halting the spread of cancer in the body.  

More Information

The following video was taken from a TED-Ed lecture by Ivan Seah Yu Jun and features animation describing how cancer spreads. For more information and resources provided during his lecture, click here.

[1]Cancer Research UK. “How cancer can spread.”

[2]National Cancer Institute. “Metastatic Cancer.”

[3]David Nield. “Scientists have finally figured out how cancer spreads through the bloodstream.”

CMN Hospital