"All the training and exercising I’ve put in is paying off," singer wrote. "[The doctor] did say, however, that I’m not quite ready for Vegas" Barry Manilow has once again postponed his upcoming Las Vegas shows as the singer works his way back from a lung cancer diagnosis late last year. In a message to fans Friday, Manilow said he received “good news” following his latest doctors appointment, but he’s still unable to return to the stage just yet. “I went to the doctor yesterday and he said I’m making great progress and look great! Well of course I do! Thank you very much! All the training and exercising I’ve put in is paying off,” Manilow wrote. “He did say, however, that I’m not quite ready for Vegas. That means I won’t be able to return for our May shows at [Las Vegas’ Westgate].” Please see the message below from Barry: Good news! I went to the doctor yesterday and he said I’m making great progress and look great! Well of course I do! Thank you very much!…