Derek Lowe comments on the news that Pfizer's (now discontinued) inhaled insulin (Exubera) had led to an increased chance of lung cancer in clinical trials. Considering the difficulties and risks of drug development, it's hard to guarantee outcome of clinical trials, especially when they should take into account that disease often happens on the order of years, not months. "The truth, as far as I can see, is that no one can guarantee the safety of a new drug.