Cancel final parts of endless sadistic massage (5)
I believe the answer is:
scrub
'cancel' is the definition.
(scrub can mean to cancel or erase)
'final parts of endless sadistic massage' is the wordplay.
'final parts of' suggests the final letters (I've seen 'final part of' mean this).
'massage' becomes 'rub' (rub can mean to massage).
The last letters of 'endless sadistic' are 'sc'.
'sc'+'rub'='SCRUB'
(Other definitions for scrub that I've seen before include "Abandon" , "Vegetation consisting of stunted trees or bushes" , "Clean by rubbing really hard" , "Rub hard; brushwood" , "Eliminate" .)