Disclosed herein are diagnostic and prognostic methods for determining drug sensitivity and resistance in Ewings sarcoma patients. Treatments for drug-resistant Ewings sarcoma are also disclosed. The assays involve the detection of GSTM4 gene expression alone or in combination with other clinical factors. The tests are suitable for diagnosing and monitoring treatment of patients having or suspected of having Ewings sarcoma. The disclosure also relates to inhibitors of GSTM4 for the treatment of Ewings sarcoma, including drug-resistant forms thereof.
