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Cancer is a disease that occurs when abnormal cells grow uncontrollably.

When detected and treated early, cancer doesn’t necessarily cause life threatening complications. Cancer becomes life threatening when it affects major organs and their ability to function.

Keep reading to learn how cancer progresses, how cancer kills, and what treatments can slow its progress.

Our bodies are constantly producing new cells to replace older or damaged cells. It’s a natural process of growth, division, and death.

Our immune systems are usually able to handle the abnormal cells we produce from time to time.

Cancer develops when abnormal cells don’t die off but continue to reproduce and evade the immune system response.

As a result, each generation of cells becomes more abnormal. These cells build up in the form of solid tumors that can spread to nearby tissue.

Cancer cells can break off from the primary tumor to form new tumors. If they reach the bloodstream or lymphatic system, they can travel throughout the body. The cells are then able to form new tumors in organs and tissue far from where it started. This process is called metastasis.

Blood cancers don’t normally result in solid tumors, but they can metastasize and cause life threatening complications.

Depending on the organ in which it starts, cancer that’s diagnosed and treated in the early stages is usually not life threatening.

Cancer can kill when it invades essential organs, like your liver, lungs, or brain, and stops them from functioning properly.

These complications could be due to primary cancer that starts in an essential organ, such as brain cancer. Or it could be cancer that has metastasized from one area to another. For example, breast cancer that has spread to the lungs.

As cancer spreads throughout the body, it becomes more difficult to control. Some types of cancer tend to spread slowly. Other types spread more aggressively.

Let’s take a closer look at some of the complications that cancer can cause.


Malnutrition is a major cause of mortality in advanced cancer. This can happen when tumors in the digestive system form a blockage or interfere with the absorption of essential nutrients.

In addition, cancer and cancer treatments can lead to loss of appetite and the inability to keep down food.

Signs of malnutrition include:

Malnourishment can affect a person’s response to treatment and overall survival.

Lack of oxygen

Tumors in the lungs can block part of the lung or cause it to collapse.

A diseased or collapsed lung can lead to:

Liver damage

The liver has many important jobs — such as filtering toxins from the blood and maintaining the balance of chemicals.

Liver tumors can prevent the liver from performing these functions, which can lead to jaundice and other life threatening issues.

Signs that your liver isn’t working well include:

Too much calcium

Cancer in the bones can cause too much calcium (hypercalcemia) to be released into the bloodstream.

This can affect the proper functioning of the heart, kidneys, and muscles. It can also cause neurological symptoms, such as confusion, memory loss, and depression.

High calcium levels can lead to coma or death.

Problems with blood and blood vessels

Cancers that push into blood vessels can cause serious damage. In the brain, this can lead to a stroke.

Cancer that affects bone marrow can interfere with the production of:

  • red blood cells, which carry oxygen throughout the body
  • platelets, which are needed to stop bleeding
  • white blood cells, which are needed to fight infection


Several factors can raise the risk of developing serious infections, such as:

  • malnutrition
  • lack of white blood cells
  • tumors in the lungs that make it hard to fight any type of pneumonia

With cancer, there’s a lot of emphasis on early detection — for good reason.

It’s easier to treat cancer at an early stage, before it has the chance to spread and cause complications. That’s why it’s so important to get routine cancer screenings and to discuss any concerns you may have with your doctor.

Treatment for advanced metastatic cancer is targeted at slowing the growth of cancer cells and stopping it from spreading further, as well as symptom management.

Treatment is based on the type of cancer, where it has spread, and what complications have developed.

In most cases, a combination of treatments is needed, which may need to be adjusted from time to time.

Systemic treatment

Systemic treatments are those that target the whole body, not just one specific area. Some of these treatments are taken intravenously (through an IV) and some are oral medications.

Chemotherapy drugs are used to target and attack cancer cells anywhere in the body. This therapy is used to slow the spread of cancer. It’s also used to shrink tumors that are interfering with major organs or causing pain.

Some types of cancer can be treated with immunotherapy, which helps your own immune system identify and attack cancer cells.

Hormone therapy, also known as endocrine therapy, is used for cancers that are dependent on certain hormones to grow, such as:

Some therapies that are more targeted may also be used for specific types of cancer. For example:

  • Signal transduction inhibitors are used to treat some types of chronic leukemia. This therapy blocks signals that are passed between molecules in a cell, which can interfere with how cancer cells divide and grow.
  • Proteasome inhibitors can treat multiple myeloma. This type of drug helps stop protein recycling within a cell, causing the cell to die.
  • Monoclonal antibodies can work with some, but not all cancers. These laboratory-produced antibodies may help restore or mimic the body’s immune system attack on cancer cells.
  • Angiogenesis inhibitors can be used to prevent blood vessels from supplying blood to some types of cancer tumors.

Localized therapy

Localized therapies treat a particular part of the body, either to slow the growth of cancer or to relieve symptoms.

Surgery to remove tumors can help improve the functioning of organs or relieve pain and pressure. Surgery may also be needed to clear the digestive tract or kidney obstructions.

Radiation therapy can target a specific area to destroy cancer cells and shrink tumors.

A variety of drug therapies and complementary therapies can help relieve some of the most common side effects of cancer treatment such as:

  • loss of appetite
  • stomach upset, nausea, or vomiting
  • constipation and diarrhea
  • pain
  • fatigue
  • shortness of breath
  • anxiety or depression

Clinical trials

Clinical trials are studies that evaluate the safety and effectiveness of new treatments that aren’t yet approved for general use.

Your doctor may be able to help you find trials that are a good fit for your type and stage of cancer.

Cancer can kill when tumors affect the function of major organs. Life threatening complications can also occur due to malnutrition, a weakened immune system, and lack of oxygen.

Cancer treatments can prevent some of these complications, as well as disease progression.

Cancer is often survivable, especially when treated in early stages. Discuss cancer risk factors with your doctor and find out what screening tests are appropriate for you.