Android APK deletes save game files on new install

I've got an app that builds out a save game file. However each time I build a new version of the app and install it, it blows away the save game file with the new install. I'm not sure if this is behavior when installing from an APK or if installing an update from the app store would leave the saved game file untouched or do the same thing.

Does anyone know? And if it's always going to blow away the data, how does one keep the saved game files from getting deleted between updates?

Thanks