There has been a growing realization that a small number of malignant cancer stem cells are already enough to ensure a continuous supply of cancer cells. These tumor stem cells are resistant to chemo- and radiation therapy and are suspected of being responsible for metastases and cancer recurrence after apparently successful therapy.
Cancer stem cells – a small robust subset of cells in tumors – are so named because of their similarity to normal stem cells in the human body. They have the ability to continuously renew themselves and to differentiate. For some years now there has been a growing recognition that they are one cause of the emergence and growth of tumors, as well as their recurrence (recrudescence) and metastasis. These stem cells, which are also known as tumor-initiating cells, are extremely resistant and often survive chemo- and radiation therapy without damage. After a certain period of time, the cancer stem cells can reactivate. They then cause new, aggressive metastases which are difficult to treat and ultimately fatal.
Bayer researchers are therefore also looking for therapies that attack these unusually resistant cancer stem cells. In partnership with California-based OncoMed Pharmaceuticals, they are working on new drugs that disrupt signal pathways believed to be crucial to the survival of cancer stem cells. The so-called Wnt signaling pathway is one of several signaling pathways that have been identified as a possible target for attack. It is at the center of the strategic alliance between Bayer and OncoMed Pharmaceuticals. The California company has been engaged in pioneering research work in this field since its founders first discovered breast cancer stem cells. To date, such stem cells have also been identified in blood cancer, as well as in colon, prostate and brain tumors, among others.