CT scan of lungs (to rule out clot) showed 15mm lesion on sternum, well corticated. Do I need this monitored or further tests?

If it were me, I-- --would. I would want an MRI bone scan. This would give me an idea if solid or cystic, also the nuclear scan would tell me if it is active, ie: destroying bone. The scan would tell me if there is increased bone uptake, meaning the bone is actively being repaired. If @ all suspicious, have it removed. .