Air carrier First Officer reported a cargo door EICAS alert. Flight crew referenced checklist; jettisoned fuel; and returned to departure airport.

Narrative

We departed from Runway XX at ZZZ on the ZZZZZ; ZZZZZ transition. On climb-out; around 2500 MSL; we received a DOOR FWD CARGO annunciator. We leveled off at 3000 MSL (which was our cleared altitude by ATC) and then began executing the Non-Normal Checklist for the DOOR FWD CARGO annunciator displayed on the ICAS. I was the PF and the Captain was the PM at this point; and we maintained these duties for the remainder of the flight.After receiving the ICAS alert; we called ATC and notified them that we had a DOOR FWD CARGO open annunciator; and we requested vectors and a climb to a minimum safe altitude to work through our checklists. ATC gave us a heading; and we continued outbound on that heading. We divided duties at this point: the Captain ran the checklist; while I handled the radios and maintained control of the aircraft.ATC continued to vector us around; and we climbed to 4000 MSL. The Non-Normal Checklists were completed; and we had to depressurize the aircraft as part of the procedure. The Captain then contacted Maintenance Control and Dispatch to bring them into the loop and get any guidance on the situation. After discussing it with them; we all concluded that we could not verify whether the cargo door was closed and locked; and therefore we elected to return to ZZZ.Our aircraft weight at this time was around 485K; and we discussed the importance of dumping fuel since this was not a critical emergency. At this point; the Captain asked me to start coordinating with ATC to dump fuel and to request priority handling. I requested priority handling with ATC and requested a climb to 5000 MSL and clearance to a point where we could dump fuel to reduce our aircraft weight. I also relayed our souls on board and fuel remaining. ATC cleared us to ZZZ to hold on the 180 radial inbound with right turns and 10-15 mile legs. I built the hold to the north of ZZZ and coordinated that plan with ATC. The controller had originally intended for us to hold south of ZZZ; and I had missed that in his call. We then entered the hold and dumped fuel until we reached our max landing weight of 445K.Once we reached this weight; we notified ATC that we were ready for vectors back to ZZZ. We again relayed our souls on board and hours of fuel remaining. ATC then gave us vectors for the ILS to Runway XXL; and we completed the arrival uneventfully. We taxied clear and exited the runway at 1. We were met by Crash Fire Rescue and notified them that we did not require further assistance. We were then cleared to taxi back to the gate. We debriefed the flight and situation at the gate and coordinated with Operations at ZZZ and the Chief Pilot.