The investigators propose a multi-institutional open label phase I/II trial of ganetespib in combination with sirolimus in patients with refractory sarcoma including MPNST. Hsp90 inhibitors and mTOR inhibitors have also both demonstrated benefit in a variety of preclinical bone and soft tissue sarcoma models. The investigators hypothesize that these agents that work on separate and potentially synergistic pathways will also be beneficial for other refractory bone and soft tissue sarcomas. Thus, the phase I component will be open to patients with refractory sarcomas, which will also expedite enrollment. Upon determination of the recommended dosing, a phase II study will be conducted. The phase II study population will be limited to patients with a diagnosis of MPNST.