Breen admits Hammers mistake
The former Coventry defender was a free agent after the 2002 World Cup, and turned down a host of clubs to move to Upton Park.
However, the Irish stopper failed to hold down a regular place in Glenn Roeder's side, culminating in last summer's move to Sunderland.
The Black Cats currently lie fourth in the First Division, despite a slow start, with Breen a virtual ever-present in Mick McCarthy's side.
"I made a mistake going to West Ham," conceded Breen. "It never worked, but I wish them all the best.
"You play one game here and there, it's not ideal. Now I'm with Sunderland and it's going reasonably well."
Meanwhile, the Irishman has bemoaned the loss of Kenny Cunningham, ahead of the country's crunch Euro 2004 qualifier against Switzerland on Saturday.
"We're going to miss Kenny," added Breen. "He's a brilliant player for Ireland, on the pitch and off it. He's a calming influence on the squad."