The 44-year-old singer, who made her way to international fame with her 2000 dance track 'I'm Outta Love', successfully battled breast cancer in 2003, reported Los Angeles Times.
Her 'It's a Man's World Tour' was set to kick off in London on April 6 but has been cancelled until further notice.
"I feel so awful to be letting down all my amazing fans who were looking forward to 'It's A Man's World Tour.' It just breaks my heart to disappoint them," the singer said on her website.
"Now more then ever, she is determined to live by her motto 'Don't ever let cancer get the 'Best of You!'" the statement said.
"A born survivor, Anastacia has one goal and that is to make a full recovery with the support of her family, friends and everyone around her.