Simplest way to look at it is this:
1) GH doesn't directly "cause" cancer.
2) GH/IGF-1 can accelerate the spread and development of cancer once it occurs within the body. But GH is not the direct trigger mechanism. It is not carcinogenic.
Thus, if predisposed (genetically more likely) to get cancer, GH could increase your risk of developing cancer that spreads out of control before your own body corrects it, causing a health risk and requiring treatment. If you get cancer while taking GH, it wasn't the GH. It was already in your cards anyway, most likely. But the GH (increased IGF-1) may allow it to spread more aggressively.
GH increases IGF-1 levels. The anti cancer effects if things like calorie restriction, fasting and metformin are all derived from their IGF-1 lowering effects. Many of cancers are hormones driven (fed). This is why oral drug treatments can sometimes involve reducing estrogen, IGF-1, etc.