As early as 1910, radiation was known to cause skin cancer. Among the best known long-term studies are those of Japanese atomic bomb blast survivors, other populations exposed to fallout from nuclear testing (for example, natives of the Marshall Islands), and uranium miners. All cancers, whether solid tumors or leukemia (blood cancer) are preceded by a period of time before the cancer develops (i.e. a latency period). It is not precisely understood how radiation damage may lead to a cancer years later. It is likely that the radiation damage acts in combination with other factors (e.g. chemicals, genetic make-up, health, etc.) which eventually lead to the cells multiplying uncontrollably.