PIK3CA and osteosarcoma: Melanoma deficiency factor 2 (AIM2) is lowly expressed in osteosarcoma cells, and overexpression of AIM2 inhibits the levels of p-PI3K, p-AKT and p-mTOR thereby suppressing the proliferation, invasion and migration of osteosarcoma cells, a process that can be reversed by LY294002, suggesting that AIM2 is a tumor suppressor (61).