It would be very tough to get an SPA for any unconventional endpoint. If nothing else, there would be a six-month delay while they went back-and-forth with the FDA.
I'm assuming the primary endpoint would be some composite of pain reduction and multiple types of bone scan - technetium, PET (maybe both FDG and fluoride ion) and CT or even gadolinium-enhanced MRI.
I think it is unequivocal that there is no significant osteoblastic activity - what remains to be seen is if the lesions are just in stasis or are actually healing.