MTOR and chondrosarcoma: mTOR signalling was previously shown to be important in chondrosarcoma41 and we confirmed that metformin decreased mTOR activity in all but one chondrosarcoma cell lines tested, which is in line with findings in other studies.19 Interestingly, mTOR activity was not inhibited in HT1080 which is the most sensitive for metformin treatment, suggesting that mTOR inhibition alone cannot explain the impact of metformin on chondrosarcoma cell viability.