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What is Metastasis and Metastatic Cancer?


When a patient receives a cancer diagnosis, they probably wonder how advanced the disease is. In order to determine the severity of the disease, you must determine if the cancer has already spread throughout the body.

Cancer spreading – what does it mean?

Metastasis is the term used to describe the spread of cancer cells from the place where they started (the primary tumor) to other parts of the body. Metastases are detected in almost half of patients who are diagnosed with cancer and are the most life- threatening event in patients with cancer. Metastases cause about 90% of all cancer-related deaths.

The main goal of the cells in the metastatic primary tumor is to create a microenvironment or an area rich in vascular networks. The cells work to make this microenvironment in a new body part, which can provide them with the necessary nutrients and oxygen to survive and keep spreading. This helps the cancer cells reproduce and form macroscopic malignant secondary tumors, which is known as metastatic cancer.

How can metastatic cancer be detected?

Metastatic cancer can be detected by performing common cancer screening tests such as laboratory tests, imaging, endoscopy, biopsies, and more. When a cancer diagnosis is suspected, the doctor prescribes the most appropriate diagnostic test to confirm or reject the diagnosis and determine if metastasis is present.

If more than one malignancy is detected, the doctor will perform a microscopic observation of the site’s cancer cells. The metastatic cancer cells have the same characteristics as the primary tumor, unlike different or independent tumor cells, which have different features. This is how doctors tell that the cancer has spread to another part of the body.

Further, metastatic cancer has the same name as the primary cancer. For example, liver cancer is cancer that started in the liver and bladder cancer is cancer that started in the bladder. When bladder cancer spreads to a region like the liver, it does not mean that the patient has both liver and bladder cancers. However, bladder cancer is considered a primary tumor and the tumor detected in the liver is called metastatic bladder cancer.

How does a cancer cell metastasize?

There are three ways cancer cells spread. They may grow directly into nearby tissues surrounding the tumor, they can travel through the lymph system, or move via the bloodstream to nearby or distant parts of the body. Depending on how far the primary cancer has spread, two main terms are used to describe it: regional and distant metastasis.

When cancer metastasizes to a nearby organ or body part, it is called regional metastasis. If the cancer spreads far away from its original site, it’s considered distant metastasis.

The development of both metastases are a series of sequential and interrelated steps the cancer cells must complete successfully in order to survive. First, cells leave their primary tumor by detaching from it.

Then, the cells will intravasate into the circulatory and lymphatic systems, endure pressure in blood vessels, evade attack from the immune system, extravasate at distant capillary beds, acclimate to their new environment, and reproduce at a distant secondary site. This whole process is commonly called the metastatic cascade.

What types of cancer metastasize?

Unfortunately, almost all types of cancer have the potential to metastasize to almost any part of the body. However, the cancer-spreading process has been studied for decades and research has determined the types of cancers that are more likely to metastasize regionally and those that are more likely to metastasize distantly. The table below depicts the most common sites where different cancers metastasize:

Cancer type
The most common sites of metastasis
BladderBone, liver, lung
BreastBone, brain, liver, lung
ColonLiver, lung, peritoneum
KidneyAdrenal gland, bone, brain, liver, lung
LungAdrenal gland, bone, brain, liver, another lung
MelanomaBone, brain, liver, lung, skin, muscle
OvaryLiver, lung, peritoneum
PancreasLiver, lung, peritoneum
ProstateAdrenal gland, bone, liver, lung
RectalLiver, lung, peritoneum
StomachLiver, lung, peritoneum
ThyroidBone, liver, lung
UterusBone, liver, lung, peritoneum, vagina

How is metastatic cancer treated?

When cancer has spread, it is harder to treat since it becomes more resistant. Therefore, metastases are usually cured with more aggressive treatments than primary cancers are.

The metastatic cancer treatment strategy used depends on several things: the type of primary cancer, location and amount of metastasis, treatments used for the original cancer, symptoms, and the person’s general health. Treatments that may be used for metastatic cancer include chemotherapy (and other drug therapies), radiation, proton therapy, immunotherapy, surgery, and ablation therapy.

Typically, the goal of treating metastatic cancer is to control and slow growth of the metastases. However, the metastases rarely go away completely. For this reason, supportive therapies such as palliative care are often used to treat metastases. These therapies improve a person’s quality of life by relieving the side effects of cancer treatments and symptoms of the disease, but they do not treat the cancer itself.

Is metastatic cancer curable?

It is difficult to answer this question due to the complexity of metastatic cancer. Whether or not a cancer can be cured depends on many factors: the primary cancer type, sites and amount of metastases, general patient health, patient diet, patient physical activity level, and other factors. Clearly cancers that have not spread are easier to treat than metastatic ones.

However, the medical field has made incredible progress in metastatic cancer treatment, which helps patients live longer and more comfortably. For this reason it is never too late to start treatment and one should never give up even if cancer has progressed and may seem overwhelming at first.

Key takeaways

Metastasis is the spread of cancerous cells from the place where they started (primary tumor) to other parts of the body.

Almost all types of cancers are able to metastasize.

Metastatic cancer is a malignant secondary tumor formed by metastasized cells from a primary tumor.

Metastatic cancer is detected by performing common cancer screening tests such as bloodwork, imaging, endoscopy, and biopsy.

Metastatic cancer is more difficult to treat than primary cancer.

Treatment methods for metastatic cancer include chemotherapy (and other drug therapies), radiation, proton therapy, immunotherapy, and ablation therapy.

Resources:

M.A. Tracey, Y. Lin, A.J. Sanders, J. Lane, J.G. Wen, Cancer Invasion and Metastasis: Molecular and Cellular Perspective - Madame Curie Bioscience Database - NCBI Bookshelf, (2013). https://www.ncbi.nlm.nih.gov/books/NBK164700/ (accessed July 12, 2022).

C.L. Chaffer, R.A. Weinberg, A perspective on cancer cell metastasis, Science (80-. ). 331 (2011) 1559–1564. https://doi.org/10.1126/SCIENCE.1203543/SUPPL_FILE/1559.MP3.

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