The I'm Outta Love hitmaker was due to kick off her trek in London on 6 April but all gigs and appearances have been scrapped so she can concentrate on beating the deadly disease again.
A post on her Facebook.com page read: "Anastacia has sadly been diagnosed with breast cancer for the second time after having successfully survived her 2003 battle with the disease. Consequently she has been forced to cancel all performances, tours and any travel from now until further notice."
The star added: "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."
Anastacia underwent surgery and radiotherapy to combat the disease the first time around.