Nab-paclitaxel in Combination with Gemcitabine for Pediatric Relapsed and Refractory Solid Tumors

This is a research study for people who have a solid tumor that was not effectively treated by conventional therapy or for which there is no known effective therapy. This is a phase I study of a drug called nab-paclitaxel used together with gemcitabine. Gemcitabine and nab-paclitaxel will be given intravenously, once a week for 3 out of 4 weeks, for a 28-day cycle. The goals of this study are: * To find the highest dose of nab-paclitaxel that can be safely given in combination with gemcitabine without causing severe side effects * To learn what kind of side effects nab-paclitaxel given in combination with gemcitabine can cause * To learn more about the pharmacology (how the body handles the drug) of nab-paclitaxel given in combination with gemcitabine * To evaluate tumor tissue for levels of certain proteins that may help with predicting who will benefit most from treatment with nab-paclitaxel * To determine whether nab-paclitaxel given in combination with gemcitabine is a beneficial treatment for relapsed and/or refractory solid tumors