13/04/2019
*What Is Cancer?*
Cancer is a group of diseases characterized by the uncontrolled growth and spread of abnormal cells. If the spread is not controlled, it can result in death. Cancer is caused by external factors, such as tobacco,infectious organisms, and an unhealthy diet,and internal factors, such as inherited genetic mutations, hormones, and immune conditions. These factors may act together or in sequence to cause cancer. Ten or more years often pass between exposure to external factors and detectable cancer.
Treatments include surgery, radiation, chemotherapy,hormone therapy, immune therapy, and targeted therapy (drugs that specifically interfere with cancer cell growth).
*Cancer treatment*
At present, the cancer treatment is targeted at its proliferation potential and its ability to metastasis, and hence the majority of treatments are targeted at rapidly dividing cells and at molecular targets that represent the bulk of the tumor. This may explain the failure of treatments to eradicate the disease or the recurrence of the cancer. Although current treatments can shrink the size of the tumor, these effects are transient and usually do not improve patient's survival outcomes. For tumors in which the cancer stem cells play role, three possibilities exist.
*First*, the mutation of progenitor cells into cancer stem cells can lead to the development of the primary tumor.
*Second*, during chemotherapy, most of the primary tumor cells may be destroyed but if cancer stem cells are not eradicated, they become refractory cancer stem cells and may lead to recurrence of tumor.
*Third*, the cancer stem cells may emigrate to distal sites from the primary tumor and cause metastasis. Theoretically, identification of the cancer stem cells may allow the development of treatment modalities that target the cancer stem cells rather than rapidly dividing cells in the cancer. This may cure the cancer as the remaining cells in the cancer growth have limited proliferative capability. If cytotoxic agents spare TICs, the disease is more likely to relapse.
The conventional therapies may shrink the size of the tumor; by contrast, if the therapies are directed against the cancer stem cells, they are more effective in eradicating the tumor.
Although the idea of the therapies focused on the cancer stem cells may look exciting, targeting the cancer stem cells may not be easy. The cancer stem cells are relatively quiescent compared to other cancer cells and do not appear to have the hyper-proliferation signal activated such as tyrosine kinase. These make the cancer stem cells resistant to the toxicity of the anti-cancer drugs, which traditionally target the rapidly dividing cells.
*Cancer and stem cells*.(STC30)
For over 30 years, stem cells have been used in the replenishment of blood and immune systems damaged by the cancer cells or during treatment of cancer by chemotherapy or radiotherapy. Apart from their use in the immuno-reconstitution, the stem cells have been reported to contribute in the tissue regeneration and as delivery vehicles in the cancer treatments.
