Why Does Cancer Spread: Understanding Metastatic Cancer

Why Does Cancer Spread: Understanding Metastatic Cancer

According to the American Society of Clinical Oncology, an estimated 14 million people around the world will learn that they have cancer in 2018. Currently, approximately nine million people — roughly 22,000 per day — lose their lives to cancer every year. By the year 2030, it is believed that 21 million people worldwide will have cancer and that around 13 million people will die from the disease every year.1

Cancer can originate in many parts of the body. It can also spread locally and more distantly. When it spreads and appears in distant organs, it is called metastatic cancer. Sometimes referred to as advanced cancer, metastatic cancer is typically given the name of the primary cancer from which it originates, and it is often classified as stage IV.2 Therefore, if someone is diagnosed with breast cancer that has spread to the lungs, they are said to have stage IV breast cancer — not lung cancer.

What is Metastatic Cancer?

As explained above, metastatic cancer is cancer that has spread to other organs through metastasis. Metastasis is the process by which cancer cells spread to distant parts of the body.3 Metastatic cancer cells have features that resemble those of the primary cancer — not the cells that were originally there — which is how it is diagnosed.

Metastasis involves the following steps.

  1. cancer cells from the primary cancer invade nearby tissue
  2. the cells proceed through the walls of nearby blood vessels and lymph nodes
  3. cancer cells travel through the lymphatic system and bloodstream to other parts of the body
  4. the cells stop moving in blood vessels in distant locations, where they invade blood vessel walls and grow into nearby tissue
  5. the cells continue to grow into the tissue, forming small tumors
  6. new blood vessels develop, helping the new tumors to grow

Diagnosis and Symptoms

The primary way in which metastatic cancer is diagnosed is through a biopsy. As noted previously, suspicious cells in parts of the body that are distant from the primary cancer will include features of the primary cancer cells when viewed under a microscope.

As far as symptoms go, they vary widely depending on things like the type of primary cancer that is involved and the location where metastasis has taken hold. Examples of the types of symptoms that may occur include the following.

  1. When cancer metastasizes to the lungs, shortness of breath may occur
  2. When cancer metastasizes to the bone, fractures and pain may occur
  3. When cancer metastasizes to the liver, a swollen belly and jaundice may occur
  4. When cancer metastasizes to the brain, dizziness and headaches may occur

Causes and Risk Factors

Metastatic cancer is caused by a primary cancer that has spread to distant parts of the body through the bloodstream and lymphatic system. Researchers are still not certain why some cases of cancer lead to metastasis while others do not. Indeed, the biggest risk factor for developing metastatic cancer is having cancer.

Common risk factors for developing a primary cancer, which is the top risk factor for developing advanced or metastatic cancer, include the following.

  1. a personal or family history of cancer
  2. older age
  3. tobacco use
  4. alcohol use
  5. exposure to radiation
  6. obesity
  7. certain viral infections, including HPV
  8. exposure to specific chemicals

It is also very unusual for a person to develop two separate primary cancers. When another cancer is found following an initial diagnosis, it is almost always cancer that has metastasized from the primary cancer.


Some of the top treatments for metastatic cancer are the same as those that are used to treat primary cancer.


Often used in conjunction with chemotherapy or radiation therapy, which are used to shrink tumors beforehand or to eliminate remaining ones afterwards, surgery doesn’t often come into play with metastatic cancer. However, if tumors at the second site begin to cause pain or other symptoms, surgery may be prescribed.


Because chemotherapy spreads anticancer drugs throughout the body, it is a common treatment for all forms of metastatic cancer. Its main side effects are well known because they involve damage to healthy, non-cancerous cells that can cause hair loss and other symptoms. It may be used before surgery, after surgery, or on a palliative basis to provide relief from cancer symptoms.

Radiation Therapy

Like chemotherapy, radiation therapy can be delivered throughout the body.

Known as systemic radiation therapy, the radioactive particles, which kill cancer cells, tend to collect mostly in the area of the tumor and therefore may not be quite as effective in this regard as chemotherapy. External beam radiation, which involves directing radioactive energy at tumors from outside the body, and internal beam radiation, which involves directing radioactive energy at tumors from within the body, are also sometimes used.

Targeted Therapy

This type of cancer treatment seeks to identify and attack cancer cells regardless of where they are in the body. It takes advantage of differences between normal, healthy cells, and cancer cells to target and kill the latter. Because different types of cancer cause different types of genetic changes in cancer cells, this therapy can be conducted very precisely and may be a useful way to treat and ease the symptoms of metastatic cancer.


With immunotherapy, a person’s own immune system is used to fight cancerous cells. Some methods involve stimulating the immune system to work harder or more intelligently; others involve giving the patients’ immune system components like manmade immune system proteins to boost immune functioning. Another method involves using so-called immune checkpoint inhibitors to allow the immune system to identify and attack cancer cells. Advanced research is currently focusing on cancer vaccines that show promise in the fight against all forms of cancer, including metastatic cancer.4

In addition to traditional treatments, many patients turn to alternative treatments for treating and easing the symptoms of metastatic cancer. Such treatments are wide-ranging and include things like acupuncture, art therapy; yoga, meditation, and massage therapy. Although research still needs to be done about the efficacy of various alternative treatment methods, many doctors encourage patients to try them because it helps them to take a more proactive role in their treatment. Many alternative methods also provide relief from common symptoms of metastatic cancer.5


Many exciting advancements are in the works in the world of cancer treatment, and many of them show promise for the treatment of metastatic, or advanced, cancer. Cancer vaccines, which are made from patients’ own cancer cells, are at the forefront of such advances. Provenge, a cancer vaccine that treats prostate cancer that has metastasized, was the first to be approved by the FDA. Clinical trials for similar cancer vaccines treating brain, lung and breast cancer are currently underway.6