PIK3CA and cancer: Although Sardinian population is considered genetically homogeneous, the results obtained in the present study may represent a clear indication that: a) differences into the genetic background - related to distinct patients’ origin within the island - may account for different mutation rates in candidate cancer genes (in our series, KRAS and PIK3CA), even at somatic level; and b) mutation frequency for any candidate cancer gene needs to be accurately evaluated in each geographical area.