The study enroll a large population of approximately 252467 participants. The study would analyze association of cancer and pioglitazone in 2 cohorts based on the usage of pioglitazone. Participants in were originally planned to be followed-up from January 1, 1997 to December 31, 2005. Based on the discussion with advisory board, it was recommended to increase the study population and duration of follow-up. The follow-up period was extended to June 30, 2012 for the study.