When the band Asia takes the stage at the iWireless Center on Monday, April 3, they'll be without singer/bassist John Wetton.

Wetton is undergoing a new chemotherapy cancer treatment that he says prohibits him from flying. The flight restriction will force Wetton to miss the first two months of the summer tour. The singer hopes to rejoin the tour in May.

In the interim, Billy Sherwood from Yes will fill in for Wetton at the April and May tour dates. Sherwood himself was a fill-in for Chris Squire in Yes before Squire's passing from cancer in 2015.