Spanish epidemiologists and geologists have found associations between esophageal cancer and soils where lead is abundant, lung cancer and terrains with increased copper content, brain tumor with areas rich in arsenic, and bladder cancer with high cadmium levels. These statistical links do not indicate that there is a cause-effect relationship between soil type and cancer, but they suggest that the influence of metals from the earth's surface on the geographical distribution of tumors should be analyzed.
