"I'm very happy to be here at such a historic club".
Perez joined the Gunners in 2016 for £17.1m from Deportivo, making 21 largely cameo appearances in 2016/17 before he was sent back to the La Liga side.
Sanchez, who has over 80 caps for his country, spent a year ago on loan at Espanyol.
The 29-year-old has signed a three-year deal with the Hammers, having spent the last two seasons with the Gunners. West Ham has great fans and plays in an fantastic stadium, so to sign here brings me great joy.
"From the very first meeting I had with Lucas, he made it very clear that he wanted to come to West Ham United and, for us, this is very important".
"I wish you all the best for the future and I hope you can go on and achieve great things". But the Baggies are still hoping they can land the worldwide midfielder with the lure of playing in what could be a very exciting season as they battle for promotion back to the Premier League.
But Press Association Sport understands a transfer across London to join the Hammers is edging closer as Thursday's transfer deadline approaches, with Perez wanting another chance to make his mark in England.
Financial details of the deal were not disclosed, but local media said West Ham had paid about 4 million pounds for the Spaniard.
"His style is different from the other strikers we have available to us, and that gives the manager more options for our attacking play", Husillos said.