It's hard to tell at that advanced stage, but it appears to be a branch removal scar instead of a canker, as the latter tends to be sunken, discolored (often darker), and sometimes oozing sap. The swollen ring in the center of the scar is callus tissue, which is the way trees and shrubs "heal" (seal-over, really) injuries that break through the protective bark layer. Eventually, it will fully close-over and become less obvious the older the tree gets (as the trunk widens). Nothing needs to be done about it at this point. Since the ring of callus tissue normally forms over top of a short stub, not on the trunk itself, that may indicate that the branch had been broken off by wind or physical injury, or a cut was made too close to the trunk. It's also possible no branch used to grow there, and that it was just an old trunk injury instead that is mostly sealed.

Miri