About five among the cases treated have deep depression (8)
I believe the answer is:
crevasse
'deep depression' is the definition.
The definition and answer can be both natural objects as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'about five among the cases treated' is the wordplay.
'about five' becomes 'rev' (I am not sure about this - if you are sure you should believe this answer much more).
'among' indicates putting letters inside (inserted letters are placed among others).
'treated' indicates anagramming the letters.
'cases' with letters rearranged gives 'casse'.
'rev' put inside 'casse' is 'CREVASSE'.
'have' is the link.
Can you help me to learn more?
(Other definitions for crevasse that I've seen before include "Deep glacial crack" , "climbing hazard in glacier" , "cold break" , "Sever sac (anag)" , "Crack in a mountain slope or a glacier" .)