Previously, no targeted agents have been able to cause tumor regression in a genetically engineered MPNST mouse model or human MPNST. Recently published data from Dr. Cichowski's laboratory demonstrated using Hsp90 inhibitors to enhance endoplasmic reticulum stress coupled with the mammalian target of rapamycin (mTOR) inhibitor sirolimus led to dramatic tumor shrinkage in a transgenic MPNST mouse model, which correlated with profound damage to the endoplasmic reticulum and cell death. Ganetespib is a novel, injectable, small molecule inhibitor of Hsp90 and is currently being investigated in adults with a broad range of tumor types with a favorable safety profile and promising early results. Ganetespib has been studied in preclinical in vivo models with a variety of targeted agents with no marked apparent pharmacological interactions. Sirolimus is a commercially available orally administered mTOR inhibitor and is the active metabolite of temsirolimus, which is FDA approved agent for advanced metastatic renal cell carcinoma. Sirolimus has been studied and tolerated in combination with multiple cytotoxic and targeted agents in a variety of tumor types. Based on strong preclinical rationale, the investigators hypothesize that ganetespib in combination with sirolimus will cause tumor regression in patients with refractory MPNSTs.