What are cancer stem cells?

Karen Jung
26 January 2018

Above: Image © luismmolina, iStockPhoto.com

Scientists are conducting some fascinating research involving cancer stem cells, non-specialized cells within a cancerous tumour. What are they finding? To understand, let’s first look at what cancer is, what stem cells are, and what cancer stem cells are teaching scientists about curing this often deadly disease.

What is cancer?

Normally, cells in your body will divide in a very organized, controlled way. But cells in the bodies of most people with cancer have somehow become able to divide uncontrollably.

In some tissues or organs in the body, the cancer cells can eventually form a lump, or a tumour. This tumour can then prevent one or more organs from working as they should. Some cancers, like leukemias (blood cancers), don’t form tumours. Instead, they cause an overgrowth of blood cells. This, too, prevents the body from functioning normally.

Did you know? In 2015, cancer killed 8.8 million people around the world. The Canadian Cancer Society estimated that around 79,000 Canadians died from cancer in 2016.

Scientists used to think all the cells in a tumour or cancer would behave the same way. Many scientists thought that one drug, perhaps combined with another type of treatment, would kill all the cancer cells and cure the person.

Eventually, scientists discovered that all the cells within a tumour are not the same! This phenomenon is called intratumoural heterogeneity, and it’s found in almost all types of cancers. So if scientists want to cure cancer, they need to understand just how different cancer cells can be.

Stem cells: afraid of commitment

Most cells in our bodies have specific jobs, and their jobs will not change. They are specialized (or committed) to be a particular type of cell, such as a blood cell or a skin cell, as long as they live. When these cells divide, they will make more cells like themselves. In other words, these new cells have the same committed function as the original cell. For example, a macrophage, a blood cell that engulfs pathogens, will multiply and divide to make more macrophages during an infection.

But stem cells have an amazing ability: they can become different cell types! In other words, they have not committed to any particular type of cell or function yet. One type of stem cell, somatic stem cells, exists in our bodies to replenish and generate the different types of cells within a tissue or organ. Somatic stem cells have committed to that tissue or organ, but not to a specific role within it.

For example, a blood stem cell can commit to being any type of blood cell: a macrophage to fight infections, or a red blood cell to provide oxygen to our body. What they become depends on what your body needs.

And because these somatic stem cells are so important and useful for our organs, they tend to live longer and have special mechanisms to defend themselves against damaging agents, like drugs.

Cancer stem cells: the evil twin

How does this relate to cancer?

Well, remember intratumoural heterogeneity? Here’s what scientists found when they looked at individual cancer cells within a tumour or cancer:

  1. Most cancer cells divided to make more cells like themselves. However, some cancer cells could divide into cancer cells different from themselves.
  2. Different cancer cells had different life spans.
  3. Different cancer cells responded differently to the same drug.

Sound familiar?

Cancer stem cells are a special group of cells within a tumour or cancer that have many of the same traits as normal somatic stem cells. As of 2017, some scientists are strongly hypothesizing that cancer stem cells are one reason that cancers are made up of different cells, and can be so difficult to treat.

Did you know? Cancer stem cells were first discovered and demonstrated to exist in leukemia cells in 1994 by Canadian scientists John E. Dick, Tsvee Lapidot, and their team at the University of Toronto.

Getting to the “stem” of the cancer

Sometimes, during treatment, the available cancer drugs and treatments will kill most or all of the cancer cells and cure the patient. Too often, however, the cancer will relapse (come back). Relapse often happens because of cancer stem cells that have escaped treatment. This means they’re able to regenerate (regrow) the tumour or cancer.

Currently, scientists like me are trying to learn everything possible about normal and cancer stem cells, looking for new ways to kill the cancer stem cells. But there is still a lot of information that we don’t know. One question we are trying to address is: where did the cancer stem cells come from? Did they come from normal stem cells in the body? Or did they come from other cells that have been modified to have these stem cell traits? We have our work cut out for us!

Did you know? As of 2017, scientists and doctors are testing new drug treatments for leukemia that try to target and kill cancer stem cells in the patient’s blood.

Fortunately, since 2008, a cancer research fundraising initiative, Stand Up 2 Cancer, has raised over $370 million for cancer research. Some of your favourite celebrities have been involved - people like Bradley Cooper, Justin Timberlake and Taylor Swift, amongst many others. And in 2016, a Canadian group of scientists led by Dr. Peter Dirks (University of Toronto) and Dr. Samuel Weiss (University of Calgary) received research funding to form the “Stand Up 2 Cancer Canada Cancer Stem Cell Dream Team” to target brain cancer stem cells. Better understanding normal stem cells, cancer stem cells, and intratumoural heterogeneity will hopefully allow scientists to kill all cancer cells more effectively in the future.

Canadian dream team to probe stem cell link to brain cancer (2016)
I. Semeniuk, Globe and Mail

World Health Organization

Stem cell basics
US National Institute of Health

US National Institute of Health. Are stem cells involved in cancer?
C.A. Goldthwaite, Jr., National Institutes of Health

Karen Jung

Thoroughly inspired by an undergraduate Co-op breast stem cells and breast cancer research position, I have been involved in breast cancer research ever since. As a fourth-year student, I conducted an honours research project in small molecule inhibitors for breast cancer cells. Following graduation, I worked for a year as a Research Assistant performing breast cancer molecular biology research and then decided to pursue a Master’s Degree in Experimental Medicine, specializing in a breast cancer transcription factor. I got married to my wonderful husband after my Master’s Degree, and moved to Edmonton, AB, where I pursued my PhD in Oncology at the University of Alberta, continuing my passion for breast cancer transcription factors. During my PhD, I gave birth to our two beautiful boys, and ended up writing and defending my PhD thesis during my second maternity leave! Our little family ultimately decided to return home to Vancouver, where I began my Post-doctoral training studying breast cancer cell integrins.