number of innovative media projects, including the Perceptions of Promise art exhibition (shown at the Glenbow Museum in Calgary and McMaster University in Toronto in 2011), the educational website Stem Cell School, and StemCellTalks, a series of symposia aimed at fostering high school students’ interest in stem cell research.
SCN issues regular press releases that are available from the website, and SCN annual reports and policy papers are also available for free download from the website. The SCN blog, Signals, provides news and information about stem cells written for a general readership, and SCN also uses social media, including FaceBook, Twitter, and LinkedIn, to inform the public about SCN activities. Information about past and present SCN-funded activities is available on the SCN website through a searchable funding database (including all projects from 2001 forward) and a searchable project database.
Sarah E. Boslaugh
Kennesaw State University
See Also: Cancer Stem Cells: Overview; International Society for Stem Cell Research; McCulloch, Ernest; Till, James.
Further Readings
Bubela, T., A. Strotmann, R. Adams, and S. Morrison. “Commercialization and Collaboration: Competing Policies in Publicly Funded Stem Cell Research?” Cell Stem Cell, v.7/1 (July 2, 2010).
Longstaff, H., C. A. Schuppli, N. Preto, D. Lafrenière, and M. McDonald. “Scientists’ Perspectives on the Ethical Issues of Stem Cell Research.” Stem Cell Review, v.5/2 (June 2009).
Stem Cell Network: Signals. http://www.signalsblog.ca (Accessed April 2014).
Stem Cell Network: The Stem Cell Charter. http://www.stemcellfoundation.ca/en/act/charter (Accessed April 2014).
Cancer Stem Cells: Overview
Cancer Stem Cells: Overview
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Cancer Stem Cells: Overview
Cancer is caused by a complex interplay of molecular signals. Uncontrolled cellular growth, a hallmark of cancer, may hold the key to understanding the spread of disease. Tumors form and proliferate from the actions of a small population of unique cells. The observation that cancer cells and stem cells share many similar properties has led to the search for “cancer stem cells.”
Cancer Cells Arise From Stem Cells
Stem cells are distinguished from other cells by two characteristics: (1) they can divide to produce copies of themselves, or self-renew, under appropriate conditions, and (2) they can differentiate into more specialized cell types. The ability to self-renew gives stem cells long life spans relative to those of mature, differentiated cells. It has therefore been hypothesized that the limited life span of a mature cell makes it less likely to live long enough to undergo the multiple mutations necessary for tumor formation and metastasis.
Increasing evidence supports a cancer stem cell (CSC) hypothesis—that cancer is initiated by a small population of tumor-initiating cells exhibiting stem cell–like properties. The characterization of CSCs will likely play a role in the development of novel targeted therapies designed to eradicate cells resistant to current chemotherapy regimens. The stem cell theory of cancer proposes that among all cancerous cells, a few act as stem cells that reproduce themselves and sustain the cancer, much like normal stem cells normally renew and sustain our organs and tissues, while cancer cells that are not stem cells cannot sustain an attack on our bodies long term. The idea that cancer is primarily driven by a smaller population of stem cells has important implications. For instance, many new anticancer therapies are evaluated based on their ability to shrink tumors, but if the therapies are not killing the cancer stem cells, the tumor will soon grow back (often with a vexing resistance to the previously used therapy).
What Are Cancer Stem Cells?
CSCs are tumor cells, with properties similar to normal stem cells, such as the ability to give rise to all cell types found in a particular cancer sample. CSCs are tumor-forming cells and may generate tumors through the stem cell processes of self-renewal and differentiation into multiple cell types. Such cells are proposed to persist in tumors as a distinct population and cause recurrence and spread of tumor by giving rise to new tumors. Cancer stem cell research is focused on developing methods to control the disease by targeting these cells.
CSCs, unlike the other cells that form the bulk of a tumor, can self-perpetuate and produce progenitor cells that can repopulate tumor cells eradicated by treatments such as chemotherapy or radiation. These properties allow cancer stem cells to resist all sorts of treatments including chemotherapy, radiotherapy, and molecular-targeted therapy. Evidence of CSC existence is much stronger for hematologic malignancies because this area is better researched as compared to solid organs.
Figure 1 Stem cell characteristics
There are two models for CSC renewal. The cancer stem cell model refers to a subset of tumor cells (CSCs) that have the ability to self-renew and are able to generate the diverse tumor cells. It is believed that only these cells can generate a tumor. The clonal evolution model postulates that tumor cells with a growth potential are selected and expanded. Cells in the dominant population have a similar potential for initiating tumor growth. In the clonal evolution model, all undifferentiated cells have similar possibility to change into tumorigenic cells.
Figure 2 A normal cellular hierarchy comprising stem cells at the apex, which generate common and more restricted progenitor cells and ultimately the mature cell types that constitute particular tissues
Figure 3 In the cancer stem cell (CSC) model, only the CSCs have the ability to generate a tumor, based on their self-renewal properties and proliferative potential
Figure 4 In the clonal evolution model, all undifferentiated cells have similar possibility to change into a tumorigenic cell
Research Related to Cancer Stem Cells
If cancer stem cells are the primary driver of cancer growth and metastasis, then effective cancer treatments must attack the CSCs in addition to eliminating the bulk of the tumor. Shrinking a cancerous tumor or reducing leukemic cells in the blood may offer temporary relief, but it will not offer a long-term cure if CSCs are not eliminated. Furthermore, if only the CSCs are eliminated, the rest of the cancer cells in the body might be attacked by the immune system or die out naturally. The most effective cancer treatments, therefore, will be those that specifically target CSCs. Discovering such treatments will require that we know as much as possible about the qualities and behavior of CSCs.
