premise: My Dad 's youngest brother passed away yesterday afternoon . He turned 69 on July 3 . About 3 years ago , he was diagnosed with lung cancer but they were successful in treating it , supposedly got it at an early stage , through both surgery and radiation . This past winter , though , he had a very bad bout with bronchitis and was in a great deal of pain . In May , the doctors diagnosed a return of the cancer , this time in his bones and even in his brain . What may have caused your dad 's youngest brother to pass away ?
hypothesis: The doctors failed to treat his cancer when it first appeared .