B757 flight crew reported during initial climb they got an EICAS message for a leading-edge slat asymmetry during flap retraction. They decided to return to the airport.

Narrative

During the initial climb from ZZZ on the ZZZ Departure from Runway XXR at the 1 intersection; we received a LEADING EDGE SLAT ASYM EICAS message during flap retraction from Flaps 5 to Flaps 1. ATC had cleared us to climb to 10;000 feet; but we requested to level off at 5;000 feet in order to run the appropriate checklist and troubleshoot the issue. We executed the LE SLAT ASYM checklist from the QRH and slowed the aircraft to remain within the flap speed limitations.As the checklist advised a landing with Flaps 20; we contacted Maintenance Control and Dispatch via ACARS and jointly determined that the safest course of action was to return to ZZZ. Due to the flap configuration and associated speed limitations; continuing to ZZZ1 was not operationally feasible.A [priority handling request] was made to ZZZ Approach; during which we provided souls on board and fuel on board; and advised ATC of our return. ATIS received and we were vectored for the ILS XXL approach.The Captain briefed the flight attendants and instructed them to prepare the cabin. The passengers were informed as well; with emphasis that the return was precautionary and the situation was under control.We completed the remainder of the checklist; configured the aircraft for landing; and upon check-in with ZZZ Tower; confirmed that we were a [priority] aircraft. Airport rescue and Firefighting (ARFF) was standing by on arrival. We landed safely; advised the Tower that no assistance was needed; and taxied to Gate XX.At the gate; we were met by Maintenance and a representative from the Chief Pilot's office. Appropriate logbook entries were completed; including documentation for the LE SLAT ASYM condition and the overweight landing.