We usually think of leukemia as a disease of the bone marrow. Sometimes leukemia is found in other locations throughout the body. For most of these locations, chemotherapy that we give is effective in getting there and treating the leukemia as well. However there are places where there appear to be barriers between the regular blood supply and the location/organ's supply. These are called "sanctuary sites" because the leukemia uses those areas to hide. These barriers prevent the chemotherapy from penetrating well. So if leukemia gets in there, regular chemotherapy is not as successful at treating the leukemia. If leukemia cells are in a sanctuary site, we must treat those areas independently.

The testicles are considered a sanctuary site for ALL, as is the central nervous system. Because chemotherapy does not penetrate the testicles well, other treatments such as radiation therapy are considered. Because patients who develop a relapse in sanctuary sites are at higher risk for recurrence of disease elsewhere, chemotherapy may be considered for treatment of these other areas. In a complicated situation such as this, a pediatric specialist at a cancer center should be consulted.