STAT3 and osteosarcoma: Other types of stem cells such as the stromal adipose-derived mesenchymal stem cells stimulate tumor growth and invasion of osteosarcoma cells, by activating the signal transducer and activator of transcription 3 (STAT3) signaling pathway, resulting in an increase of the expression of matrix metalloproteinase (MMP) 2 and MMP9 [32].