Why is cancer so hard to cure?

By Jessica Saenz

Today, we know more about cancer than ever before. More treatments are available to patients than at any other time in history, and researchers make discoveries about how to prevent and treat the disease every day. Yet, some types of cancer are increasing and, in some cases, affecting younger age groups.

Why does cancer continue to outsmart us?

Mark McNiven, Ph.D., a Mayo Clinic researcher who holds the George M. Eisenberg Professorship II, says the answer isn’t a single silver bullet. He and Tanios Bekaii-Saab, M.D., a Mayo Clinic medical oncologist and the David F. and Margaret T. Grohne Professorship of Novel Therapeutics for Cancer Research I, explain how cancer works and why it's so hard to cure:

What is cancer?

Cells in the body follow instructions that determine every function in their life cycle, from division to purpose to death. "Normally, when cells reproduce to a certain number or density, they signal to each other to stop growing," says Dr. McNiven, director of the Mayo Clinic Center for Biomedical Discovery and co-leader of Mayo Clinic Comprehensive Cancer Center’s Cancer Cell Genomics, Signaling and Metastasis Research Program. When a change or mutation occurs in a cell, it may begin to disregard instructions and multiply erratically. This process is known as cancer.

So, how does this disregard for instructions become deadly? The repercussions of uncontrolled cell growth differ for each cancer type, but Dr. McNiven says the result is often organ failure. "Each cell in our body has a particular function. When cells become cancerous, they no longer function as if they were from that tissue or organ of origin. They turn into nondescript cells that accumulate, grow and take nutrition from your body," he says.

Cancer isn’t one disease: it's many diseases.

Cancer is a broad term encompassing many diseases that stem from the unchecked growth of cells. But even within one type of cancer, there can be many variations that respond to different treatments. These variations are called cancer subtypes.

"If you take a tumor and slice it into multiple pieces and look at the genetic composition — even within that same tumor — we are likely to find different subpopulations of cells with different genetic compositions. And that likelihood increases as the tumor grows," says Dr. Bekaii-Saab, chair of the Division of Hematology and Oncology at Mayo Clinic in Arizona and chair of Mayo Clinic Comprehensive Cancer Center’s Gastrointestinal Cancer Disease Group.

Dr. Bekaii-Saab says cancer specialists used to think they could treat each cancer type the same way. "But it turns out that each type of cancer has to be broken down into multiple groups. And with each of those small subgroups, we have a specific target that appears to be most relevant for the originating cancer type," he says.

Not all cancer subtypes have a treatment. That's because cancer scientists are still discovering gene alterations linked to cancer and researching drugs that could affect their function. Still, Dr. Bekaii-Saab says researchers have made significant progress in recent years, and the pace of research is accelerating. "The world of targeting cancer at the genetic and molecular level is moving fast. Finding targets and translating research into the clinical setting — it's moving at an astronomical rate and will likely accelerate further with the integration of artificial intelligence and machine learning."

Early detection is critical to curing cancer but isn’t always possible.

The possibility of a cure is highest when cancer is caught at its earliest stage when it can be removed surgically or targeted with treatment. Regular screening can lead to early detection or even prevention of certain cancers such as colon and breast cancer. "More than half of patients diagnosed with cancer will survive longer than 10 years. That's increased from a much smaller percentage two decades ago, partly because we're detecting cancer earlier, but also due to significant advances in treatment options," says Dr. Bekaii-Saab.

But not every cancer causes symptoms — or symptoms that are easily distinguishable from other health conditions. And screening tests aren’t yet available for every cancer.

Uterine cancer, for example, is the most common gynecologic cancer, but no standard screening test exists. People are encouraged to report unusual symptoms to their healthcare professional and keep up with annual pelvic exams. If uterine cancer symptoms are subtle, mistaken for symptoms of other health conditions, or nonexistent, then the cancer has time to progress into later stages.

While most cancers may not be curable in later stages, Dr. Bekaii-Saab says treatment advances mean people with cancer can often live a meaningful life span. "Patients' lives are being prolonged, and their quality of life improves significantly if we find the right treatment match. Although we're not curing them at this stage, and cancer will likely take their life at some point, we're extending their survival and preserving their quality of life for many years."

Treatments must fit each person — and their cancer.

Each cancer is unique, and so is each person diagnosed with cancer. When developing cancer treatment plans, care teams consider cancer type, subtype and stage, the general health of the patient, and the patient’s preferences. Treatments must be effective in killing the cancer while also being well tolerated by the patient.

Most treatments carry risks, but as your cancer team designs your care plan, they can help you weigh the risks and benefits of cancer treatment to help you determine what you are comfortable with and what's most important to your quality of life.

Weighing risks and benefits includes considering other health conditions (comorbidities) to determine if treatment could complicate them. "We must consider different genetic drivers, previous exposures, comorbidities and other factors so we can treat everyone with the right level of care," says Dr. Bekaii-Saab.

Lack of representation in clinical trials and access to cancer care has hindered progress.

Clinical trials help medical researchers understand how to diagnose, treat and prevent cancer and other diseases and conditions. Historically, people from minority populations have had limited access to clinical trials.

"For the last 100 years, we have focused most of our studies and treatments around white men of Northern European descent, but that is only part of the population," says Dr. McNiven. "It turns out that people respond differently to treatments based on their heritage and genetic makeup, where they live, and what they eat."

Increasing participation of people from diverse populations in clinical trials can help researchers learn more about cancer cures for everyone.

Dr. Bekaii-Saab says matters that might seem small to some — like transportation, time off work or even parking fees — can be barriers that prohibit people from accessing cancer care and clinical trials. "If we want to achieve true health equity and representation in clinical trials and cure more cancers, we have to think about how to make clinical care and research trials more accessible."

Learn more

Learn more about cancer treatment and find cancer clinical trials at Mayo Clinic.

Join the Cancer Support Group on Mayo Clinic Connect, an online patient community moderated by Mayo Clinic for patients and caregivers.

Also, read these articles:

• Clinical trials: A significant part of cancer care
• Dear Mayo Clinic: 5 advances in cancer treatment
• Reduce your risk for the 4 most common cancers
• Dear Mayo Clinic: Genetic counseling after cancer diagnosis