Today, cancers that respond to treatment are not considered outright cured because there is always a potential they could come back. Instead, they are referred to as being in complete remission or evaluated as having no evidence of disease (NED), meaning there is no detectable cancer in the body.
In terms of what the future holds for curing cancer altogether, some experts believe evolving treatments may, one day, make that a reality. Others think the ability to control cancer as a chronic disease is more achievable.
Either way, the many types of the disease and differences in those living with them will significantly factor into this effort, meaning there can't be a one-size-fits-all approach to curing cancer.
This article examines the possibility of a future cure for cancer. It explains the complexities of the disease, obstacles that prevent the cure of more cancers, and the ways in which advances in research and treatment may eventually deliver success.
Treatable vs. Curable
Even if a cancer cannot be considered 100% eradicated today, many can be effectively "cured" if detected early.
Stage 0 cancers such as ductal carcinoma in situ (DCIS) are, in theory, cancers that can be cured completely.
Oncologists (cancer specialists) will also refer to someone as "cured" if they had acute lymphoblastic leukemia as a child because the likelihood of recurrence in adulthood after successful treatment is low.
The following are types of cancer that are considered more "curable" based on five-year survival rates
- Breast cancer
- Melanoma
- Thyroid cancer
- Hodgkin lymphoma
- Testicular cancer
- Prostate cancer
But there are important nuances to this, too.
For example, stage 1 to stage 3 breast cancers that are estrogen receptor positive are more likely to recur five to 10 years after diagnosis than in the first five years. Sometimes recur even decades later.2
These cancers may be more "treatable," as there are more options for keeping them in check than there are for other cancers. But they are, in a sense, less "curable" than those that are not hormone receptor positive.
Durable Response
In some cases, the term durable response may be used when it appears long-term control of a metastatic cancer is possible or achieved. This is most common in stage 4 cancers that respond to treatment, with immunotherapy drugs appearing to improve the chances of durable response.
One Goal, Many Targets
A big part of why cancer cannot be completely cured right now is that cancer is not one thing.
There are hundreds of different types of cancer, from the all-too-common but highly treatable non-melanoma skin cancers to the rare and aggressive Merkel cell carcinoma, a different type of skin cancer that's often fatal.
Even when two cancers are the same tissue type, subtype, and stage, they may still have significant molecular differences that play a role in treatment options and outcomes.
Pharmacogenomics—knowing how a person's genetic make-up influences how they respond to drugs—is still an evolving area of personalized medicine sciencce.
Further, cancer cells often find ways to escape both treatments and the immune system.
The Promise of Similarities
Cancer isn't one disease, but scientific advances are exploiting some of the similarities between different cancers in order to treat them.
Cancer cells begin as normal cells in the body, making them much more difficult to treat than other microorganisms. But the changes that cause this transformation, and the pathways associated with them, often overlap among cancer types.
Roughly 90% of cancer-related deaths are due to metastases (original cancers that spread to other parts of the body). The ways in which errant cells spread to regions they don't belong are somewhat consistent among tumor types.
For example, cancer cells often lose proteins referred to as adhesion molecules that cause them to stick to nearby cells.4 This makes the cells more likely to break loose and travel via the blood or lymph fluid to other parts of the body.
Shared Treatments
The immunotherapy drug Opdivo (nivolumab) and the targeted therapy drug Vitrakvi (larotrectinib) are based on these discoveries and, therefore, work for more than one cancer type.
Opdivo (nivolumab)
This checkpoint inhibitor works to make cancer cells visible to the immune system, eliciting a response to fight them. It is approved for people with cancers including:5
- Metastatic non-small cell and small cell lung cancer
- Melanoma skin cancers
- Liver cancer
- Hodgkin lymphoma
- Head and neck cancer
- Kidney cancer
- Certain forms of colorectal or esophageal cancer
Vitrakvi (larotrectinib)
This targeted therapy drug works in some people with cancer who test positive for a genetic change called neutrophic receptor kinase (NTRK) gene fusion. It may be used to treat people with:6
- Salivary gland tumors
- Sarcomas
- Thyroid cancer
- Colon cancer
- Lung cancer
Obstacles in Curing Cancer
Aside from the fact that cancer is not one thing, the continually changing nature of cancer, resistance to treatments, and other challenges continue to be roadblocks on the road to a cancer cure.
Cancers Change
There's a tendency to think of cancer as an unchanging clone of abnormal cells, but that's not the case at all. Cancer cells are continually changing and acquiring new mutations.
These new mutations may give rise to new characteristics of the cancer, such as the ability to spread more freely. Non-genetic cellular changes in cell behavior, called epigenetic changes, also occur.
Resistance
Changes in cancer cells mean that a tumor that responded to treatment at first has found ways to resist cancer drugs and continue to grow.
A significant amount of cancer research is focused on the growth pathway of specific tumors to identify other targetable places to halt their growth.
Many targeted therapies are able to control the growth of a tumor for a time before resistance develops. In some cases, next-generation drugs are available that allow people to stay ahead of this resistance, but tumors often change again.
Resistance also can transform a tumor into a completely different subtype of cancer. For example, some EGFR positive non-small cell lung cancers may transform to small cell lung cancer, a much more difficult type of cancer to treat.
Cancers Enlist Help
Cancer cells often hide and adapt while enlisting help from normal cells in their surroundings.
These nearby cells, such as fibroblasts and macrophages, can be coaxed into helping a tumor grow through blood vessel growth (angiogenesis) that feeds the tumor or suppresses the immune system.
Their secretions can't be studied in a lab, further complicating researchers' ability to understand them.
Heterogeneity of Tumors
Not all cancer cells are the same, at the same time. They continually change how they behave and adapt in different parts of a tumor. This is called heterogeneity.
Due to these changes, one part of a tumor may be sensitive to a treatment while another part of the tumor (or a metastasis) may be resistant.10
Balance: Efficacy vs. Toxicity
Treating cancer means establishing a balance between what's effective and its side effects. This balance is visible when adding immunotherapy drugs to cancer treatment.
The immune system requires a balance between being overly active and attacking the body's own tissues, and being underactive such that tumors grow unchecked.
The most common side effects of immunotherapy drugs include inflammatory disorders, while reciprocally, some medications for inflammatory diseases may raise the risk the cancer.11
Research Limitations
Most cancer drugs are first studied in the lab and in animal studies. What works in a dish in the lab (in vitro) does not often translate to effectiveness in the human body (in vivo).
According to a 2018 review, it's thought that roughly 90% of cancer drugs that appear to be effective in lab studies fail to work when studied on humans in clinical trials.12
The cost of research is also an influencing factor that cannot be ignored.
Treatments and Advances Toward a Cure
Progress in curing cancer may seem slow, but several advances in diagnosis and treatment are changing cancer care.
Targeted Therapies
Targeted therapies, while not a cure, can sometimes control a cancer for a significant period of time. Gleevec (imatinib) used to treat leukemia and a few other cancers is a good example.
With second and third generation drugs for some types of cancer, some people—at least for a time—control their cancer as a chronic disease much like high blood pressure or diabetes.
The ability to identify gene mutations and rearrangements is expanding. Tests such as next-generation sequencing allow healthcare providers to examine many genetic alterations that may be treatable.
Immunotherapy
Sometimes a person may experience the spontaneous remission of cancer, even an advanced cancer. It's now thought that the immune system may fight off a cancer in some cases.
The immune system knows how to fight cancer with powerful cells such as T cells. Unfortunately, cancer cells have discovered the ability to suppress that immune response so that cancer cells can grow unchecked. Immunotherapy drugs work to empower the immune system instead.
Immunotherapy drugs known as checkpoint inhibitors make cancer cells visible to the immune system. These drugs can result in durable responses in advanced cancers like melanoma, but they don't work for everyone. Future research may find ways in which more people will respond.
One notable finding is that the diversity of gut bacteria (the gut microbiome) relates to how well checkpoint inhibitors work.13 Research into ways to increase diversity of the gut microbiome is needed to see if these drugs can be effective for more people.
Adjunct Therapy
Immunotherapy in combination with radiation treatment can sometimes improve control due to the abscopal effect. Cell death from radiation activates immune cells that then attack tumor cells far away from the site where radiation was delivered.These combined therapies with an added (adjunct) treatment may improve outcomes.
Nanotechnology
Nanotechnology is a way of detecting and treating cancer at the molecular level using nanoscale devices. These are very small, between 100 and 10,000 times smaller than a human cell.
Scientists hope one day these tiny devices will be used to detect cancer at the earliest possible stage. Nanoscale devices can also be used to deliver targeted therapies directly to cancer cells and to help guide surgeons during tumor removal.
Cancer Vaccines
The same mRNA technology that was used to create COVID-19 vaccines is also being tested for cancer treatment. An mRNA cancer vaccine could target specific proteins found in cancer cells and be individualized for a person's specific type of cancer.
In theory, these vaccines will be able to help the immune system learn to recognize the cancer cells as invaders so they can be eliminated.This technology has been used in clinical trials with mixed and sometimes disappointing results.
More than 20 mRNA-based vaccines entered clinical trials by 2021, with some promising outcomes in treating solid tumors.
Treatment of Oligometastases
Sometimes a metastatic cancer may be reasonably controlled by treatment, but a new metastasis starts or continues to grow (a "rogue" tumor).
Treatment of these areas with methods such as stereotactic body radiotherapy (SBRT) with a curative intent may sometimes eradicate these rogue tumors, allowing a cancer to again be controlled.
The Future of Finding a Cancer Cure
There are many approaches both already available and in the works that promise to improve cancer care and perhaps, one day, a cure. For example, some people respond particularly well to certain treatments.
Researchers want to know why a rare person might respond to a treatment. One example is the EGFR inhibitor Iressa (gefitinib), which was limited 20 years ago to only people with non-small cell lung cancer who responded well.
The evolving understanding of the role of EGFR mutations in some lung cancers (between 10% and 20% of non-small cell lung cancers) led to expanded drug approval in 2015, for people with specific EGFR-related changes.
While two main types of EGFR changes account for 85% of those identified, researchers continue to work on more rare types, like EGFR exon 20 insertion mutations.
Other research priorities that may change the way "cure for cancer" is understood include:
- Understanding recurrence, or how and why cancer cells may hide and return
- Understanding metastases, which can lead to new treatments like
- bisphosphonates in breast cancer
- Liquid biopsies, which can offer new insights into tumor resistance
New genetic discoveries also may lead to prevention or early detection of cancers, as well as treatment options. Genome-wide association studies are studies that look at people with and without a disease and then look for changes (called single nucleotide polymorphisms) in the entire genome that may be associated with the disease.
What About CRISPR?
Gene editing (CRISPR-Cas9) is certainly advancing the science that could aid in treatments, but it's unlikely that gene editing alone could be a cure in the near future. More potential could be seen in the use of CRISPR to edit cells in the immune system to better fight cancer as with strategies like CAR-T immunotherapy.20
Summary
While cancer can't be cured, that's not how oncologists and cancer experts think about a successful treatment. They refer to it as complete remission, allowing for the fact that cancers can recur. They also describe it as "no evidence of disease" that, in some cases, may prove permanent.
Advances in cancer treatment aren't the same as a cure, but they are helping people to live longer with a cancer diagnosis—sometimes even with the hope of managing it as a chronic disease.
Evolving research continues to deliver more personalized care, including immunotherapy and targeted therapy drugs. New understanding about cancer and its treatment already informs cancer care and offers options that weren't possible even a few years ago.
