In a nutshell, what is paget's disease of the bone?

Benign usually. Bone enlarges, can be painful, rarely can lead to malignancy.
Which one. Paget's disease is a disorder that involves abnormal bone destruction and regrowth, which results in deformity.The cause of paget's disease is unknown, although it might have to do with genes or a viral infection early in life. There is another one called paget disease of the breast. Good luck thanks.