As you age, it's common to lose bone density. Your body doesn’t replace the cells that rebuild your bones as quickly as it used to, leading to thinner bones with small holes, known as osteoporosis. Certain conditions can put you at risk for osteoporosis earlier in life, such as multiple myeloma. Multiple myeloma is a cancer of the plasma cells in your bone marrow. It disrupts the balance between building new bone and breaking down old bone, increasing bone breakdown while slowing new bone formation. This can cause