Cancer is almost unspeakably awful, from the potential hardships of treatment to the prospect of leaving behind grieving loved ones. This horrible illness has a sweeping reach. An estimated 1.7 million people in the United States were diagnosed with cancer in 2018, according to the National Cancer Institute (NCI). Around 610,000 people were estimated to die from the disease by the end of the year.
While the emotional and physical tolls of cancer are often clear, it can be confusing as to how, exactly, cancer kills someone. Is it due to the cancer itself? Or is it usually a more indirect result of how cancer can affect a person’s health? And does it vary depending on the type of cancer a person has?
This can be a terrifying topic to discuss with a doctor or loved one, depending on your situation. But sometimes you need answers to even the scariest questions. Here, we spoke to several oncologists to explain how cancer can lead to death.
Cancer happens when cells grow out of control.
It can be easy to forget how intricate human biology is, but your body is made up of trillions of cells. In order to function properly, these cells are constantly growing and dividing to form new cells, the NCI explains. In the normal cellular cycle, cells that become old or damaged die off and get replaced by newer, healthier versions.
Cancer forces this usual process to go terribly wrong. If someone has cancer, their old and damaged cells don’t die off, and new cells form without reason. These cells can start to divide uncontrollably and, as a result, form tumors, the NCI says.
Cancer is more likely to be fatal when it's metastatic, meaning it has spread throughout the body.
You might have heard of metastatic cancer but not known exactly what it means.
Metastatic cancer happens when cancerous cells disperse into surrounding tissues or even travel to other parts of the body through the blood or lymph systems, according to the NCI. These cells can then form tumors in their new locations.
Even though metastatic cancer has by definition moved from its point of origin, it’s still considered a form of that primary cancer, the NCI explains. So, if you had ovarian cancer that spread to your stomach, it would be considered metastatic ovarian cancer, not stomach cancer.
It’s often this spread—and its impact on one or several major organs—that ultimately kills someone, Jack Jacoub, M.D., medical oncologist and medical director of MemorialCare Cancer Institute at Orange Coast Medical Center in Fountain Valley, California, tells SELF. For this reason, cancer staging is largely dependent on how extensively the cancer has traveled. Stage IV cancer, the most severe form, means the cancer has wound up in distant body parts.
But metastatic cancer doesn’t kill people in any one specific way. Instead, this disease can take a few avenues to end someone’s life.
These are the complications that are most likely to be fatal for someone with cancer.
1. Malnourishment or dehydration
Cancer can interfere with the function of your all-important digestive system, which is comprised of organs like your stomach, pancreas, and intestines. Tumors can clog up this system, creating obstacles that don’t allow food or food waste to get through, the NCI explains. That, in turn, can cause issues such as frequent nausea and vomiting. But cancer-related digestive issues are most likely to become life-threatening due to malnourishment or dehydration.
“The body stops being able to use nutrients properly,” Martin J. Edelman, M.D., deputy cancer center director for clinical research at Fox Chase Cancer Center, tells SELF. This means that even if someone is receiving nutrients via IV, they can still die from malnourishment.
Malnourishment can be accompanied by difficulty maintaining fluid levels. “Dehydration is almost universally a side effect of advanced cancer,” Ishwaria Subbiah, M.D., assistant professor in the department of palliative care and rehabilitation medicine at The University of Texas MD Anderson Cancer Center, tells SELF.
While doctors can give a patient with advanced cancer IV fluids, at a certain point, it’s difficult for the body to hold onto these necessary liquids. “The fluids don’t stay where they’re intended to stay, and will seep from the blood vessels into surrounding tissue,” Dr. Subbiah says. This can lead to dehydration.
2. Respiratory failure
Whether cancer originates in the lungs or affects these organs after becoming metastatic, this disease can kill off healthy lung tissue or block off portions of it, making it far too hard to breathe, the NCI says.
Someone with advanced cancer may receive oxygen in a facility like a hospital. But that doesn’t necessarily fix the problem if their lungs can’t properly inhale, exhale, or transport oxygen and carbon dioxide through their respiratory system. So, over time, a person with advanced cancer can have too much difficulty maintaining the oxygen levels that their body needs to survive, and their organs can begin to fail as a result, Dr. Subbiah says.
Cancer can also create infections that cause the lungs to fill up with fluid, which can then prevent a person from getting in enough oxygen over time, Dr. Subbiah says.
3. Loss of brain function
If cancer impacts the brain, it can lead to loss of consciousness, seizures, and the brain’s general inability to perform the way it needs to, Bryan McIver, M.D., Ph.D., deputy physician-in-chief at Moffitt Cancer Center, tells SELF. Brain bleeding or injury that harms the function of another critical body part, like the lungs, can also kill someone, the NCI says.
Another complicating factor: The brain is in the contained space of the skull, so there’s nowhere for it to go if it swells due to pressure from a tumor, Dr. Subbiah says. “In certain cases, the pressure is so high that it leads to a herniation where part of the brain slips down from the base of the skull,” she says. “That’s [almost] always fatal.”
4. Bone marrow issues
Cancer can spread to the bone marrow, the matter in the center of large bones that makes new blood cells. If this happens, it can lead to a host of life-threatening issues.
A lack of sufficient red blood cells can bring about anemia (not having enough oxygen in your blood), which can kill someone if severe enough. If your bone marrow can’t create enough platelets to help your blood clot, it’s harder to prevent dire levels of bleeding.
Cancer in your bone marrow can make your levels of white blood cells designed to help fight infection drop to precipitously low levels, the NCI says. On a related note, some cancer treatments such as chemotherapy can incapacitate a person’s immune system, thus raising their risk of life-threatening infection, according to the American Cancer Society (ACS).
“Serious infections like sepsis can be deadly, although someone can have a more [local] infection like pneumonia or a urinary tract infection that could [become] serious,” Dr. Edelman says. The likelihood of this varies based on the type of cancer someone has, Dr. Edelman says. But, in general, people with cancer in blood-forming tissues, like leukemia, are often most at risk because the cancer can more easily kill off too many white blood cells.
6. Blood clot complications
Unfortunately, cancer and cancer treatments can generally increase a person’s risk of developing blood clots, according to the ACS. There’s also the fact that a person with advanced cancer is often in bed for long periods of time—another blood clot risk factor. Together, this can raise a person’s odds of developing a blood clot that may lead to a deadly stroke or pulmonary embolism (a clot that blocks blood flow in the lungs), Przemyslaw Twardowski, M.D., professor of medical oncology and director of clinical research in the department of urology and urologic oncology at John Wayne Cancer Institute at Providence Saint John’s Health Center in Santa Monica, California, tells SELF.
7. Liver failure
Your liver juggles a lot of important jobs including separating toxins from your blood and helping you to digest food, the NCI explains. Cancer that starts in or spreads to your liver can cause this organ to fail and have trouble completing these duties. Eventually, this can cause life-threatening complications like excessive bleeding, including in the GI tract, and blood infections, the Mayo Clinic says.
8. Excessive calcium levels
When cancer damages a person’s bones, too much calcium can leach into their bloodstream, the NCI says. That’s a condition known as hypercalcemia, and it can devastate the heart and brain’s abilities to work properly, according to the Mayo Clinic. This means that, in severe cases, hypercalcemia can lead to coma and death.
Early detection and treatment often lower the odds of these complications.
While doctors can treat some of these problems as they happen in otherwise healthy people, it’s much more complicated in those with advanced cancer, Dr. Subbiah says. Often, several things are going wrong at the same time, which is why advanced cancer so frequently has deadly consequences. As Dr. Subbiah explains, “These are not fixable problems when you put them all together.”
That doesn’t mean that all of these complications are unavoidable or even always deadly when they do happen. They’re much more common and harmful with advanced cancer, the experts explain, which is why early detection and treatment are of the essence. It’s also why there is hope for many people with cancer, especially in the earlier stages.
“The [overall] rate at which people are dying of cancer has fallen,” Dr. McIver says. “We’re getting much better at avoiding direct cancer deaths. And, even when cancer can’t technically be cured, it can often be controlled for many years and even decades.”