Treat back sores, running somewhat (5)
I believe the answer is:
nurse
'treat' is the definition.
(nursing is a kind of treating)
'back sores running somewhat' is the wordplay.
'back' is a reversal indicator.
'somewhat' indicates a hidden word.
'esrun' is hidden in the letters of 'sores running'.
'esrun' reversed gives 'NURSE'.
(Other definitions for nurse that I've seen before include "Suckle" , "Nightingale" , "Hospital worker" , "Hospital employee" , "One skilled in caring for the sick" .)