I really believe that Doctors tend to stereotype people. They look at a person, and decide what the problem may be based on age, gender, race etc. If Trent was too young to statistically have that tumor, or if it was very rare for his gender/race etc., they would never look for it.
My wife almost died of a ruptured appendix because she was misdiagnosed in the ER with Crohn's. After many days, when her white cell blood count was off the charts, they decided to operate, and found the ruptured appendix. They seemed to believe that A white female 60 yrs old should not have had that, so she was never examined or asked about that.