A 63-year-old asymptomatic woman is seen in the clinic for investigation of a persistently elevated alkaline phosphatase (ALP) level. The elevated ALP is an isolated finding and the remaining liver enzymes are normal. She reports no abdominal symptoms suggestive of biliary colic or hepatitis.On physical examination, the vital signs are normal, she is not icteric, the heart sounds are normal and the lungs are clear. The abdomen is soft and the liver span is 12 cm in the mid- clavicular line.X-rays of the pelvis show multiple porotic and sclerotic lesions with characteristic whorls of trabeculation. Her excretion of urinary hydroxyproline is also elevated. Which of the following is the most likely diagnosis?