Possible Explanations for Tolerance

• Large, rapidly-growing tumors are thought to outstrip the blood supply and result in the death of tissues from a lack of oxygen and other nutrients. Large numbers of tumor cells dying and breaking away from a growing primary mass might be mistaken by the immune system distal to the primary tumor as a signal that the existing responses are sufficient to eliminate the tumor, resulting in a premature attenuation of the immune response. This is particularly problematic when any viable tumor cells being released are strongly adherent.
• Accurate gauging of the needed response also is dependent upon the relative numbers of released cells that are metastatic. When the vast majority of cells succumbing to anoxia are normal, an additional erroneous signal might be sent, i.e., that too violent of an immune response is already underway, resulting in further attenuation of the immune response.