The role of GIS in cancer epidemiology would be interesting.  The geographic pattern of cancer is so different. For example, nasopharyngeal carcinoma is common in Southern China. Recently I met Chinese girl from Henan province(northern part) . We had brief conversation on her province and health condition. I remembered, while reading epidemiology of  esophagus cancer, we had mentioning of Henan province. Probably, it has to do with p53 gene mutation, which is more common in indigenous population of Henan!