About Solid Tumour Cancers

Are there stem cell treatments available for solid tumour cancers?

Hematopoietic stem cell transplants from bone marrow and umbilical cord blood have been approved by Health Canada and the U.S. Food and Drug Administration to help treat patients with solid tumours. Patients who are researching their options may come across companies with websites or materials that offer other types of fee-based stem cell treatments for curing a variety of different solid tumours. Many of these claims are not supported by sound scientific evidence and patients considering these therapies are encouraged to review some of the links below before making crucial decisions about their own treatment plan. However, the field of cancer research is fast-moving and work underway today may uncover new possibilities for more effective treatments tomorrow. Therefore, is is important to keep asking questions and to continue seeking advice from qualified experts.

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How close are we? What do we know about solid tumour cancers?

  • A tumour refers to any abnormal growth of cells. Tumours can be benign (harmless) or malignant (dangerous).
  • Solid tumours grow as a mass of cells in a particular organ, tissue or gland, most commonly thebreast, lung, prostate, and colon.
  • Solid tumours have different names depending on where they grow: carcinomas develop in skin cells or cells lining or covering the internal organs; sarcomas develop in bone, cartilage, fat, muscle, blood vessels or connective tissue; lymphomas develop in mature immune system cells. Brain tumours generally do not fall into these categories, as they may arise from cell types exclusively found in the brain.
  • Some risk factors for solid tumours can be modified (smoking, exercise, weight, alcohol use, exposure to hormone medication) while others cannot (age, gender, family history).
  • If solid tumours are benign and stay in their place of origin, they can generally be removed and pose no long-term threat. However, malignant tumours are able to metastasize or spread to another part of the body via the blood or immune systems. If that happens, the prognosis becomes poor.
  • The standard of care for the treatment of solid tumours includes surgery, radiation, chemotherapy, adjuvant stem cell transplantation, and immune therapy.
  • Despite many advances, the vast majority of metastatic solid tumours are still incurable.

How can stem cells play a part?

The application of stem cells to treat solid tumours revolves around two basic approaches: transplanting hematopoietic stem cells (blood cells that can give rise to all types of blood cells), and learning about cancer stem cells. Hematopoietic stem cell transplants have been used for many years to resupply blood cells to patients undergoing chemotherapy or radiation as part of their cancer treatment. These can either be autologous (from the patient) or allogeneic (from a donor). Both types of transplants are used to treat patients with solid tumours. For example, allogeneic transplantation combined with reduced intensity chemotherapy has been successful in decreasing relapse rates in some solid tumours, such as breast and kidney.

Autologous transplantation is particularly useful in pediatric cancer. Children are not candidates for radiation as it would damage their young, developing brains, so their hematopoietic stem cells are harvested and re-infused following aggressive chemotherapy. This approach is now standard and can increase survival rates for children with brain, bone, and immune cell tumours.

A new and exciting field of research aims to understand how cancer stem cells are involved in tumour formation and metastasis, and to develop therapies that target them and prevent relapse.

Are there lots of groups working on developing a stem cell therapy?

There are countless research teams around the globe working to develop stem cell therapies for solid tumours. They are focused on developing novel methods for taking advantage of hematopoietic stem cell transplantation, identifying additional sources of these cells, and applying the knowledge learned from studying cancer stem cells to treat cancer patients.

Hematopoietic stem cell transplants – commonly called bone marrow transplants – date back to the 1950s and ultimately led to cures for lethal forms of leukemia. This tremendous accomplishment paved the way for these blood-forming stem cells to be used as an adjuvant, or helper, therapy for treating patients with solid tumours as well. Other important milestones include the development of drugs to prevent the host from rejecting the graft, and finding ways to prevent the graft from attacking the host (called graft versus host disease, or GVHD). However, GVHD is not all bad because immune cells present in donor hematopoietic stem cell transplants can also attack tumour cells in the patient, and oncologists now take full advantage of this benefit to kill solid tumour cells.

Stem cell research for solid tumours is unfolding along a number of different avenues and some of the successful results are being translated into early Phase 1 and 2 clinical trials. The majority of these trials test the broadening applications of hematopoietic stem cells to treat different types of solid tumours and the outlook is promising. Researchers are also grappling with the tremendous variation in solid tumours that they are seeing within individual cancer patients and also among different patients with the same type of cancer. These observations have enormous implications for understanding cancer development, metastasis, and relapse. With a better understanding of the role played by cancer stem cells, scientists hope to create the tools necessary to target cancer stem cells and minimize cancer relapse.

What research is underway?

Before basic stem cell research can be translated into the clinic for patients, it must first be rigorously tested and validated. For solid tumours, the use of hematopoietic stem cells from bone marrow and umbilical cords has already gone through this rigorous process and has been clinically proven effective. Found predominantly in bone marrow, but also in umbilical cord and peripheral blood, hematopoietic stem cells are responsible for making all the red and white blood cells in the body. Much of the current research involves evaluating new ways to apply hematopoietic stem cells, and finding other sources for transplants.The road to finding a stem cell therapy for solid tumours is paved with many challenges that will take time to overcome. But the wealth of information generated from labs around the globe is converging to help with the transition from basic research to the clinic. The results are very promising and in time may point to additional stem cell therapies for treating a wide variety of solid tumours and preventing relapse.

Current research using allogeneic hematopoietic stem cell transplantaion tumours

Metastatic tumours remain largely incurable, causing 90% of all cancer deaths. New treatments are desperately needed. Years of research and clinical trials in metastatic breast cancer paved the way for researchers to test whether allogeneic stem cell transplantation could benefit other metastatic tumours, including those found in the esophagus, stomach, colon/rectum, liver, pancreas, lung, breast, prostate, bone, and kidney. Today, clinical trials are underway to test this approach in patients who do not respond to standard therapy. These patients receive what is called a ‘mini-transplant’ of peripheral blood stem cells from a brother or sister. They are also given intense immunosuppressive drugs in an attempt to reduce transplant-related side effects and to help the grafted stem cells and immune cells, called lymphocytes, thrive. The idea is to see if lymphocytes in the donor transplant can successfully attack the tumour to extend patients’ lives or even cure them.

Current research using cancer vaccines

Although chemotherapy in combination with hematopoietic stem cell transplants can lead to remission of risky cancers, there is still a high incidence of relapse and the side effects take a heavy toll on patients. To address these drawbacks, some researchers have been experimenting with cancer vaccines. Cancer vaccines are based on tumour samples from a patient or donor and are created to target specific tumour cells and proteins. The theory is that vaccinating patients with a cancer vaccine after they have received a stem cell transplant could kick start the immune system to attack any cancer cells that have remained after high dose chemotherapy. This approach is very much still at the experimental stage, but there are ongoing pilot studies in patients with different solid tumours, including brain, bone, and muscle.

Current research to find other sources of hematopoietic stem cell transplants

As the number of people with cancer increases due to the aging population, so too will the demand for hematopoietic stem cell transplants that can buffer the toxic effects of chemotherapy and radiation. While transplant registries around the world have worked nothing short of miracles in terms of matching donor-recipient bone marrow, there continues to be a shortage of suitable donor material. To address this, researchers are turning to other sources of hematopoietic stem cells. Cord blood is one approved option, but the number of hematopoietic stem cells per cord is quite low, only enough to treat a child or small adult. Strategies to address this include learning how to expand the number of stem cells from a single cord, testing molecules that can help the stem cells to engraft better, and performing double cord blood transplants.

Another potential source comes from man-made stem cells called induced pluripotent stem cells (‘pluripotent’ from the Latin words ‘very many’ and ‘having power’). Induced pluripotent stem cells, or iPS cells, can be made from a patient’s skin or other tissue cells. Their biggest asset is that the cells they make are perfectly matched with the patient. Although much work needs to be done before cells made from this technology are ready to use on the front lines of patient care, it is encouraging that scientists have already figured out a way to turn iPS cells into hematopoietic stem cells. Many pre-clinical studies are underway to test if such cells can restore blood function.

Current research on cancer stem cells>

The concept that cancers are propagated by a small subset of cells with stem cell properties has existed for more than a century. This concept is important because it implies that these cells must be eliminated to achieve long-lasting cures. However, because cancer stem cells are rare, they are difficult to identify and study. Scientists have now identified cancer stem cells in the blood, breast, brain, prostate, colon, colorectal, head and neck, lung, ovary, kidney, and skin. Many questions remain about the relevance of cancer stem cells, but perhaps the most pressing is how they are involved in metastatic tumours. Researchers are searching for biomarkers that are unique to cancer stem cells. These will be used to better sort cancer stem cells from normal stem cells, to identify cancers that have the highest risk of recurrence and metastasis, and to act as targets for new cancer therapies.

Researchers are also realizing that the field of cancer stem cells is quite complex. There is growing evidence the cells that can generate new tumours are not necessarily normal stem cells that have become cancerous, but may represent “later” cell types that have reactivated stem cell properties. As well, cancer stem cells appear to be continuously evolving into more aggressive cells as the disease progresses, and perhaps even in response to treatment pressures.

Going back to basics, researchers are starting to monitor patients throughout all stages of cancer (diagnosis, relapse prior to treatment, after treatment, relapse after treatment) to better understand how and why the number of stem cells changes during the course of a patient’s disease. They are also testing whether chemotherapy-type drugs could reprogram the non-DNA elements within a cell (called the epigenome) and in so doing possibly reverse the characteristics of cancer stem cells. This concept is being tested in very early clinical trials.

Further reading on solid tumour cancers

Readers may wish to peruse the recommended sites and articles below for more information about solid tumours and the possible applications of stem cells to treat various types of cancer.

Canadian Cancer Society
National Cancer Institute
Ontario Institute for Cancer Research