iwfal serves me right for butting in to a situation in which i am not knowledgeable. i looked up the abiraterone data and sure enough about half had bone scan flares. this did seem to be higher than other studies looking at incidence of flare after treatment, which seemed to range from 6% to 41% (part of the variability in incidence of flare may be due to timing of when bone scans were performed)
that said low or absent incidence of flare in the exel data is more a curiosity rather than something that makes me question the treatment response since it is something that leads to false positives but not false negatives (i.e. some responders have worsening bone scans initially, but few non-responders have improving bone scans)