JAY Z FILLS IN FOR THE BEASTIE BOYS @ THE ALL POINTS WEST MUSIC FESTIVAL!

Jay-Z has been tapped as a last-minute replacement for the NYC rap trio at next week's All Points West music fest in New Jersey. The Beasties backed out of the July 31 concert last Monday after group member Adam "MCA" Yauch announced he has cancer in his parotid gland and in a lymph node in his throat. Beyonce's main squeeze has never played an American music festival before.

And he's picked quite a place to start! The Brooklyn-born rap legend headlines the opening night of the three-day fest in Liberty State Park, a stone's throw from New York, topping a list of bands that includes fellow headliners Tool and Coldplay (who play the fest Saturday and Sunday, respectively), plus sets from buzzworthy acts including Vampire Weekend, the Arctic Monkeys, the Yeah Yeah Yeahs and MGMT.

The NYC-based Yeah Yeah Yeahs are replacing the Beastie Boys at Lollapalooza the following weekend (August 7-9) in Chicago's Grant Park.

Earlier this week, the Beasties announced they are canceling all of their upcoming tour dates and pushing back the release of their next album, "Hot Sauce Committee Part 1," so that Yauch can focus on getting better.

"It's a pain in the neck (sorry had to say it)," he jokes with his trademark humor on the group's website, "because I was really looking forward to playing these shows, but the doctors have made it clear that this is not the kind of thing that can be put aside to deal with later."

The band's label reports the cancer was caught pretty early and is "very treatable," so Yauch should hopefully make a full recovery.

In the meantime, Jay-Z, who's gone in and out of retirement countless times, is getting a golden opportunity to win over a rock audience with this primetime gig.

The show may even afford the hip-hop mogul a chance for a live indie crossover: His upcoming disc "Blueprint 3" will feature a collaboration with electropop act MGMT, reports Rolling Stone, and the duo will be playing the festival the same day as his set.

It seems like a fair trade-off for fans, but Festival organizers are offering refunds at the point of purchase for any July 31 single-day ticketholders that are bummed about the Beasties Boys' cancellation.