Some concrete issues that I can see with testing in Third World countries:
1. Following/compliance with proper protocol at physician level 2. Difference in controls vs. in first world (diet, health, etc) 3. Overall health levels in one vs. other 4. Difference in physiologies between different ethnic groups 5. Patient compliance
In my years studying bios, those companies trying overseas testing in third world have almost uniformly failed. Some that come to mind: ICN and ribavirin for AIDS - did eventually work for Hep C but probably delayed, SCLN for Hep C, EMIS for diabetes.