In conclusion, PI3K inhibition is an effective strategy for targeting cancer cells and overgrowth syndromes at multiple levels, but the reality of on-target toxicity in non-tumor tissues means much work remains to be done to develop new treatment strategies if this class of drugs is ever to be used as an effective part of a chronic treatment regime for cancer or overgrowth therapies. This evidence concerns the gene PIK3CB and overgrowth syndrome.