HGH will not cause bone elongation once the growth plates close.
As far as cancer, there is a theoretical risk but no study that proves HGH use causes cancer...however, the studies are all done at non-bodybuilding doses. I am a supporter of HGH use for people who are deficient, and in very mild doses. At high doses, we don't have any good research (thats why its interesting to read some of the experiences here...from gh15 and getiton)