The pharmaceutical and biotech industries have begun to develop targeted inhibitors of pathways that contribute to tumorigenesis and metastasis. These new medicines offer the promise of treating many types of cancer with greater efficacy and fewer unwanted side effects than heretofore possible. An important premise guiding this work is the cancer stem cell (CSC) hypothesis.
While normal stem cells are essential for development, play a key role in tissue maintenance, and aid in repair, cancer stem cells are believed responsible for tumorigenesis, metastases, and cancer recurrence. The first report providing evidence of CSCs identified primitive leukemic cells that could give rise to acute myeloid leukemia in immunodeficient mice.
Since that discovery in 1994, these cells have been found in most solid tumors. Skeptics of the CSC hypothesis have argued that cancer cells may be capable of de-differentiating and that isolation methods for CSCs do not select for all cells with the capacity for self-renewal. Regardless, the hypothesis provides an explanation for differences between cells in a tumor and offers a new rationale for drug design.
Moving from concept to clinic in just over a decade, CSC research has uncovered several promising pathways that a growing number of biopharmaceutical companies are exploring in clinical and preclinical studies.