Cantus was a human colony planet.
At some point before the 27th century, the Cybermen invaded Cantus, converting all humans on the planet into them. The Cybermen created tombs beneath the surface of the planet and went into hibernation.
Irving Braxiatel travelled to Cantus with a Gallifreyan crystal and placed Ronan McGinley as the Cyber-Controller of Cantus, under his control. The Gallifreyan crystal became known as the Crystal of Cantus and gave a sense of mythology to the planet.
Years later, Braxiatel needed a new Cyber-Controller, and manipulated Jason Kane into going to Cantus with him. Braxiatel installed Kane as the new Cyber-Controller. After learning that this had happened to Kane, Bernice Summerfield took the Crystal of Cantus and used it to destroy all the Cybermen on the planet. (AUDIO: The Crystal of Cantus)