Pain in both hips

Hello, 

My husband was disgnosed with stage 4 bladder cancer about 5 months ago. It has metastasized to the lung and possibly lymph nodes but he was fortunate to be treated with immunotherapy from November. He's tolerating this very well and started to feel much better, especially when he was told the pelvic area was showing good improvement.  However, immediately afterwards, he began to experience pain in both hips and thighs which is now affecting his mobility.  The medics aren't too interested - has anyone else experinced this kind of pain? 

Thank you .