How does cancer kill? How it spreads and complications

We’ve all heard the stories, and we’ve all known someone affected by it, but how does cancer kill? It’s a complicated question, But don’t worry; we’ll break it down for you.

A white Doctor treating a male cancer patient

Key takeaways:

  • Cancer, when detected and treated at an early stage, doesn’t usually kill you.
  • Cancer becomes life-threatening when it spreads to major organs, affecting their ability to function. For instance, cancer can kill when it affects the lungs, blocking off part of it and making breathing hard.
  • There is no cure for cancer yet, and the best chance of survival is early detection and treatment.

Cancer is one of the most feared diagnoses. In fact, many people equate cancer diagnosis with death.  

However, it is important to understand how cancer kills, spreads and what treatment options are available. If you are curious to learn more, read on to discover how cancer spreads and the available treatments. 

How does cancer cause death?

The way in which cancer leads to death varies depending on the type of cancer, the degree of spread and the parts of the body affected. However, in most cancers, the degree of spread (metastasis) plays a significant role in cancer death. 

As cancer spreads, it may invade essential organs like the liver, lungs, brain, or digestive organs and affect how they function. 

Here are some organs cancer may affect and how it might lead to death:

1. Bones

When cancer is in the bones, it causes too much calcium to be released into the bloodstream. This condition is called hypercalcemia.

High levels of calcium in the blood can lead to coma or, eventually, death.

Cancer can also get into the bone marrow. When this happens, it can affect the body’s ability to make healthy blood cells. 

If your body cannot produce enough red blood cells, it can lead to anemia. If it affects the production of white blood cells, then it makes it harder for your body to fight off infections. Likewise, a drop in platelet levels will make it difficult to control bleeding as the body’s clotting mechanism is impaired. Most of the time, it's a combination of factors that causes death from cancer. Anemia and severe infections can cause the failure of vital organs such as the heart and kidneys.

2. Lungs

When cancer gets to the lungs, it might block off part of the lung. If this happens, the cancer patient might find it harder to breathe or get enough oxygen. 

Cancer in the lungs can also cause the lungs to collapse, which can cause them to be infected. For people with advanced cancer, it may be harder to fight off this infection, even with a strong prescription of antibiotics. As a result, the infection may eventually lead to death.

3. Breast

Photo source: National Cancer Institute on Unsplash

According to the World Health Organization, the leading cause of death from breast cancer is widespread metastases. What this means is that death from breast cancer usually arises from complications that occur when cancer invades essential organs like the lungs, liver, or brain. 

4. Brain

When cancer is in the brain, it can affect its normal functioning, including the parts that control movement, speech, and other functions.

In cases where the brain cancer grows too large, it can press against very important structures of the brain, which can lead to headaches, vomiting, bleeding, seizures, stroke, coma, and eventually, brain death. 

5. Digestive system

If cancer spreads or is in the digestive system (e.g., stomach, pancreas, or colon), it may obstruct the passage of food or waste products, which can cause bloating, nausea, and vomiting.   

In addition, cancer in the digestive tract can interfere with the digestion and absorption of nutrients, causing malnourishment and dehydration in the patient.

If a patient is malnourished, it can also make it harder for their immune system to fight off infections, leaving them more vulnerable to illness. 

Furthermore, cancer cells could potentially break off and spread to other organs, like the lungs or liver, leading to even more complications and possibly even organ failure, which can be life-threatening.

6. Liver

The liver plays an important function in removing toxins from the blood, digestion, and producing bile. It also produces substances that help with blood clotting when there is a wound. Cancer in this organ can stop or interfere with the normal functioning of the liver leading to jaundice and fatigue. It may also cause excessive bleeding, leading to death.

As cancer advances, liver function deteriorates even further, leading to liver failure, which can lead to death. 

7. Cervix/vagina

Cancer in the cervix or vagina may break off and spread into nearby tissues like the rectum, bladder, or pelvic wall leading to bleeding, pain, and obstruction of bowel movements.

As the cancer advances, it can spread to other distant organs (distant metastases) like the lungs, liver, or brain. At this point, the cancer is often difficult to treat and becomes life-threatening. 

How cancer spreads

Cell division and growth are natural processes. The human body constantly produces new cells to replace old, damaged, or worn-out cells. The body cells are supposed to die naturally when they become old or damaged. However, sometimes something goes wrong during cell division that leads to the production of abnormal cells, or the old cells refuse to die.

These abnormal cells tend to divide faster than normal cells do, and because they don’t die as and when they should, it becomes more difficult for our immune system to fight them effectively.

As these cells continue to grow faster, they may break away from the original sites where they were produced and spread to nearby or distant organs and cells—a process known as metastasis. 

To spread to other organs, tumors travel through the bloodstream or the lymphatic system and then establish new tumors in other organs or tissues, which can make cancer more difficult to treat.

Is cancer deadly in the early stage?

Cancer can be deadly at any stage. However, studies have shown that when cancer is identified early, it is often more responsive to treatment, increasing the chances of survival.

Thanks to new and improved diagnostic and screening, cancer can be detected early and treated before it spreads to other parts of the body when it gets harder to treat.

This is why getting early detection and screening is recommended, especially if you are at a high risk of getting cancer. 

Can cancer be cured?

The answer to the question of whether cancer can be cured is not so simple.

However, to answer the question clearly, we have to define what a “cure” is.

Typically, when people use the term “cure", they mean the complete eradication of cancer without the possibility of it returning and without the need for further treatment. However, cancer treatment is not that simple. 

Instead of “cure,” most doctors prefer the term “remission” as they cannot be 100% certain cancer will not return. 

Remission is defined as a period of time when cancer is under control or responsive to treatment. In other words, what people call a cure is actually remission.

That said, although doctors cannot be 100% certain that cancer will not return, some cancers, such as childhood leukemia and Hodgkin lymphoma, have a lower chance of returning after successful treatment. 

The longer a person remains cancer-free, the better their chances of not experiencing a recurrence.

Cancer treatment

There are several cancer treatments available, and as science advances, newer treatments are being discovered.

Your treatment option will often depend on several factors, such as the stage of the cancer, its type, age, and other factors. Before you get started on a particular treatment, your doctor will walk you through the procedure and explain the risks and benefits to you.

Here are some common cancer treatments available: 


Chemotherapy is the process of using drugs to shrink or kill cancer cells. Sometimes, your doctor might recommend chemotherapy to slow the spread of cancer.

Chemotherapy can either be used alone or, in most cases, in combination with other treatment options like surgery.

Some side effects of using chemotherapy include: 

  • Fatigue
  • Easy bruising and bleeding
  • Hair loss
  • Infection
  • Anemia
  • Nausea and vomiting


Surgery involves an operation to totally or partially remove the tumor.

The surgery can be open (involving a large cut or incision) or minimally invasive (with tiny incisions).

Unlike chemotherapy, which can be used to treat cancer throughout the body, surgery is usually recommended for cancers located in a specific area. Like chemotherapy, surgery is often combined with other treatment options. 

Hormonal therapy

Some types of cancer, like breast, prostate, and uterine cancers, are sensitive to the levels of certain hormones, which means the cancer cells thrive when those hormone levels are high. Hormone therapy involves the use of medication to block the production of these hormones in order to slow down the growth of these types of cancers.

Hormone therapy is often used with other types of cancer treatment, such as chemotherapy. 


Immunotherapy, also called biological therapy, involves the use of the body’s immune system to fight cancer. 

Immunotherapy works by activating or enhancing the ability of the immune system to recognize and destroy cancer cells.

This treatment is particularly useful for treating advanced or metastatic cancer that is difficult to treat with other types of therapy. However, keep in mind that not all cancers will respond to immunotherapy.

Radiation therapy

Radiation therapy uses high-energy rays such as X-rays or protons to kill cancer cells. 

There are three ways radiation therapy is delivered:

  • External beam radiation: This involves using high-energy rays to target the tumor from outside the body. This form of therapy is often used to treat cancers that can easily be targeted from outside, like prostate or breast cancers.
  • Internal radiation or brachytherapy: This involves placing a radiation source directly into or near the tumor. The radiation source will usually remain in the patient’s body for a period of time, usually days. This form of therapy is often used to treat cancers that are located deep inside the body, such as the cervix.
  • Systemic radiation: This involves the use of radioactive drugs delivered orally or through an injection. The radioactive substance travels throughout the body and is absorbed by cancer cells. This form of therapy is often used to treat cancers that have spread to other parts of the body and are difficult to treat with surgery or external beam radiation.

Bottom line

Cancer becomes life-threatening when it spreads to major organs, affecting their function. Hence, the best chance of survival is early detection before it spreads. That’s why it is strongly recommended to get regular cancer screenings, especially if you are at high risk for the disease. By detecting cancer early, you can receive prompt and effective treatment that can save your life. 


  1. Cancer Research UK (2022). High calcium in people with cancer
  2. Cancer Research UK (2020). The immune system and cancer
  3. John Hopkins Medicine (ND). Manage Shortness of Breath with Lung Cancer
  4. World Health Organization (2021). Breast cancer
  5. National cancer institute (2022). Nutrition in Cancer Care
  6. Nigel Hawkes (2019). Cancer survival data emphasize the importance of early diagnosis