You have 2 types of cells involved with bone replacement. You body replaces the entire skeleton about every 7 years - a little at a time - all the time. The cells are osteoblasts - which make new bone and osteoclasts -which eat up old bone (that's the replacement cycle). The tumor toxin causes the osteoblasts to slow down (thus make less new bone cells. It also makes the osteoclasts eat faster. This could leave holes or parts of bone missing as the body can't replace the damage as fast as it was make. The tumors could actually be getting smaller but still producing the toxin. Damage slows down but doesn't stop right away. Once the tumors are gone and the toxin isn't there any more then it will take time for the osteoblasts to get busy enough to repair the bones. In a few cases the damage may be extensive enough that the pain never goes away totally. Usually the body does a great job of repairing damage so don't lose hope.
Ask the onc to refer you to PT so you can get knowledge of what exercises you can do to help things along and not cause further damage or increase you pain. Exercise will increase blood flow and that always helps repair cells to function better. Asking for a new scan is a good idea. If the tumors are smaller that will give you peace of mind. If they are largest you can get busy with an altered treatment plan.
Hang in there and fight like a girl!!
Take GOoD care