Body part in doctor's office (5)
I believe the answer is:
torso
'body' is the definition.
(a person's middle)
'part in doctor's office' is the wordplay.
'part in' indicates the answer is hidden within the clue.
'TORSO' is hidden within 'doctors office'.
(Other definitions for torso that I've seen before include "Body without head, neck and limbs" , "unfinished work" , "Roost (anag)" , "Body's trunk" , "Main part of human body" .)