Nab-Paclitaxel and Gemcitabine for Recurrent/Refractory Sarcoma

Inclusion Criteria: * Participants must be age ≥ 3 and ≤ 30 years, and have had a histologic diagnosis of osteosarcoma, Ewing sarcoma, or rhabdomyosarcoma or non-rhabdomyosarcoma soft tissue sarcoma either at diagnosis or relapse. Must have experienced relapse after front-line therapy, or have had documented disease progression during front-line therapy. * Must have measurable disease that can be assessed using Response Evaluation in Solid Tumors (RECIST) 1.1, defined as the presence of at least one lesion on MRI or CT scan that can be accurately measured with the longest diameter of 10 mm in at least one dimension. For this phase II trial, patients with disease limited to bone or marrow metastases are NOT eligible, as disease at these sites cannot be assessed by RECIST 1.1 criteria. * Must have relapsed or refractory cancers for which there is no known curative option. * Prior Therapy: There is no limit to the number of prior therapies provided all eligibility criteria are met. However, participants must have recovered from the acute toxic effects of all prior treatment. (A) Must not have received prior therapy with either gemcitabine or nab-paclitaxel. (B) Myelosuppressive chemotherapy: Must not have received myelosuppressive chemotherapy within 3 weeks of protocol therapy on this study. (C) Hematopoietic growth factors: 7 days must have elapsed from the start of protocol therapy since the completion of therapy with filgrastim, and 14 days must have elapsed from the start …