Update (7:28 p.m. EDT): The fight has officially been canceled, along with the rest of the card.
Dan Rafael of ESPN.com tweets this evening that an official cancellation of the May 19 fight between Lamont Peterson and Amir Khan is forthcoming, which surprises no one and at this point is merely a formality, but for those wondering still, yes, this fight is off and the word will be coming down soon.
Peterson tested positive for synthetic testosterone in March, and won't be licensed to fight by the Nevada State Athletic Commission. Golden Boy and Khan have no interest in scheduling a replacement opponent for Khan on 10 days' notice, and there's really no one viable out there who could take the spot, anyway.
Khan may return on June 30, as GBP and HBO are reportedly discussing that date. As for Peterson, this is a huge hit to his career. Yeah, he'll fight again, and probably in a good fight or three, but he's never going to be looked at the same, and his big win over Amir Khan suddenly became a lot less of a great underdog, rags-to-riches story.
We'll let you know when the fight is officially, 100%, for sure off the table by way of official announcement, but if you were holding on hope for a May 19 rematch, it's not happening.