Analog signal over long cable
STP I assume means screened/shielded twisted pair and if you want to measure current flowing down one of the conductors then do so at any point. "Condition" the signal where the measurement is made or do the conditioning half locally and half remotely. The minimum amount of conditioning to be done locally is to amplify the shunt signal so that the wires from the amplified shunt conditioning circuit do not pick-up excessive extraneous EMI on route to the final circuit that monitors the shunt current.