I too am stage 4 PC. After chemo therapy (I only did 4 rounds out of 6 prescribed) my low back pain increased to the degree of immobility. I ended up having back surgery in the middle of chemo therapy. Now have a couple of rods and screws in my back and no longer have sciatica pain. I’m not exercising ( treadmill and elliptical 4 times a week). I am currently on just ORGOVYX and have had no cancer activity since 2019