Today we'll be answering Google's most searched questions about when cancer spreads. As we'll talk about in a future article, the spread of cancer is how cancer kills so this can be a heavy topic. If you're a cancer patient, please talk to your doctor about this. Google shouldn't be where you find the answers to your questions--that should be a qualified expert who can explain the facts in the context of your disease.

Where cancer spreads

Cancer can spread almost anywhere in the body, but certain sites are more common than others. It also depends on the type of cancer. The most common sites overall are the lungs, the liver, the lymph nodes, the bones, the brain, and the skin.

One way for cancer to spread is via cancer cells getting into the bloodstream and being carried all around the body that way. If you think about it, it makes sense that the lungs would be the most common organ for cancer to spread to: all blood travels through them to pick up a fresh supply of oxygen, and cancer cells can end up stuck there. This might inspire another question about whether cancer can grow in the heart. After all, all blood also travels there. We answered this question in a past article.

Cancers of the digestive system—stomach, intestines, etc.—commonly spread to the liver for a similar reason as for a spread to the lungs. Blood in this area returns to the liver before it returns to the heart, and cancer cells can get stuck there.

It is also extremely common for cancer to spread to lymph nodes. We’ve explained how this works in a past article, but the basic are that fluids and damaged cells which are unable to enter the bloodstream for filtration later down the road are eventually picked up by another system in the body called the lymphatic system. Those fluids are then filtered in little lymphatic filtration systems called lymph nodes. Cancer cells, which are a kind of damaged cell, sometimes get stuck there and cancer begins to grow.

Prostate, breast, and lung cancers commonly spread to the skeleton. This can be dangerous and painful, as it tends to make bones weak and easily breakable.

Lung cancer and breast cancer sometimes spread to the brain. It also happens, but less commonly, with colon cancer, kidney cancer, and melanoma.

Cancer occasionally spreads to the skin near a surgical incision through which a tumor was previously removed.

When cancer spreads to lymph nodes

We’ve already talked about how cancer gets to lymph nodes. The body has hundreds of lymph nodes, and usually the closest ones to the original tumor are affected by spreading cancer. Once cancer cells reach there, the nodes tend to swell (although this also happens as a result of ear infections, colds, strep throat, and chicken pox).

Surgery is sometimes used to treat cancer that’s spread to lymph nodes. Removing them can leave a dead end where lymph used to flow, causing fluid to build up in the area. According to the American Cancer Society, this can be a problem for cancer survivors for the rest of their lives.

Where does bladder cancer spread to?

Bladder cancer can spread to lymph nodes in the pelvis and other nodes near large veins and arteries in the legs. It also commonly spreads to the lungs and bones through the bloodstream.

When cancer spreads to the bones

Almost all kinds of cancer can spread to the skeletal system, but it’s especially common with breast cancer and prostate cancer. These secondary tumors can be located in any bone, with the most common being the spine, pelvis, and femur (the bone in the thigh).

According to the Mayo Clinic, it’s unclear why cancer spreads to bone. Common symptoms are pain, fractures, urinary and bowl incontinence, limb weakness, nausea, vomiting, constipation, loss of appetite, extreme thirst, and confusion.

Unfortunately, cancer that’s spread to the bones usually can’t be cured. It is possible to stop or slow the growth of bone metastases.

When cancer spreads to the spine

As with any other bones, cancer weakens the structures and makes fractures more likely to occur. The American Cancer Society says cancer can cause bones in the spine to break and collapse, which feels like a “sudden pain in the back”. Cancer which has spread to the bones in the spine can also compress the spinal cord—a structure which extends into the back from the brain and carries messages from the brain to the body (and vice versa). Compression of the spinal cord can impair both movement and sensations, causing numbness or weakness. It can also cause trouble urinating and constipation. Depending on the location of the tumor, spinal cord compression which goes untreated can cause paralysis of either the legs or all four limbs. According to one study, spinal cord compression happens in about 20% of cases where cancer has spread to the spine.

In 21% of the times cancer spreads to the spine, the original tumor is located in the breast. Other cancers that sometimes spread to the spine are lung, prostate, renal, gastrointestinal, and thyroid cancers.

Cancer which spreads to the spine can be exceedingly painful and patients may be prescribed narcotic drugs to manage that pain.

Spinal metastasis is usually treated with chemotherapy and radiation.

When cancer spreads to the liver

Types of cancer that commonly spread to the liver are colorectal cancer, lung cancer, breast cancer, pancreatic cancer, stomach cancer, melanoma, and neuroendocrine cancer. There are two parts to the liver—called lobes—and most of the time both lobes are affected. Until liver metastases start to become relatively serious, the liver can work as normal to filter blood and take care of its other functions. Usually liver metastases are treated with chemotherapy or targeted drug therapies. Surgery and radiation don’t generally work very well for this purpose unless the cancer has spread only to very limited areas of the liver.

It is very difficult to estimate how long a person with cancer which has spread to the liver might live. It depends on the person’s medical history and overall health. Having said that, if the original tumor was in the prostate or breast, a patient with liver metastases may live for years.

When cancer has spread to the brain

The most common types of cancer which spread to the brain are lung cancer, breast cancer, colon cancer, kidney cancer, and melanoma. In fact, about 25% of lung cancer patients will experience brain metastasis. It’s unknown exactly how many cancer patients deal with cancer spreading to the brain, but studies suggest the number is between 10 and 30% of all cancer patients.

Like when cancer spreads to the bones, when cancer spreads to the brain it’s usually considered to be no longer curable, although patients with brain metastases may live as long as a few years depending on their individual medical history.

Brain metastases are generally treated with radiation and surgery. The blood vessels in the brain are very special and tightly control what can enter brain tissue from the blood. This is called the blood-brain barrier and means that most of the cancer drugs used today—including many chemotherapy drugs—cannot affect the brain. It is very difficult for scientists to design drugs which will work in the brain. Having said that, treatment for brain metastases has improved in recent years, and more clinical trials are underway.

Tumors in the brain are dangerous because they put pressure on the brain. Structurally, the brain in a skull is not terribly unlike a balloon in a glass jar; there’s just not very much wiggle room. Pressure in the brain can cause headaches, seizures, nausea, vomiting, trouble speaking, trouble seeing, and limb weakness.

Sources

Vachani, C. (2017, November 24). All About Brain Metastases. Retrieved from https://www.oncolink.org/cancers/brain-tumors/brain-metastasis/all-about-brain-metastases 

ASCO Answers - When Cancer Spreads to the Brain. (n.d.). Retrieved from https://www.cancer.net/sites/cancer.net/files/asco_answers_brain_metastasis.pdf 

Bone metastasis. (2018, April 18). Retrieved from https://www.mayoclinic.org/diseases-conditions/bone-metastasis/symptoms-causes/syc-20370191 

Finding Bone Metastases. (2016, December 15). Retrieved from https://www.cancer.org/treatment/understanding-your-diagnosis/advanced-cancer/finding-bone-metastases.html 

Liver metastases - Canadian Cancer Society. (n.d.). Retrieved from http://www.cancer.ca/en/cancer-information/cancer-type/metastatic-cancer/liver-metastases/?region=on 

Lymph Nodes and Cancer. (2015, April 14). Retrieved from https://www.cancer.org/cancer/cancer-basics/lymph-nodes-and-cancer.html 

Smith, R. P., & H, C. (2017, October 12). All About Bladder Cancer. Retrieved from https://www.oncolink.org/cancers/urinary-tract/bladder-cancer/all-about-bladder-cancer 

Understanding Advanced Cancer, Metastatic Cancer, and Bone Metastasis. (2016, December 15). Retrieved from https://www.cancer.org/treatment/understanding-your-diagnosis/advanced-cancer/what-is.html 

What Is Brain Metastasis and How Is It Treated? (2017, August 01). Retrieved from https://blog.dana-farber.org/insight/2017/07/which-cancers-are-most-likely-to-spread-to-the-brain/ 

Where cancer can spread. (2017, December 06). Retrieved from https://www.cancerresearchuk.org/what-is-cancer/how-cancer-can-spread/where-cancer-can-spread 

Ziu, E. (2017, June 27). Cancer, Metastasis, Spinal. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK441950/