At trial entry patients will be randomised to one of four chemotherapy regimens:
1. Topotecan and cyclophosphamide (TC): 6 cycles. Additional cycles may be given at the discretion of the treating clinician.
2. Irinotecan and temozolomide (IT): 6 cycles. Additional cycles may be given at the discretion of the treating clinician.
3. Gemcitabine and docetaxel (GD): 6 cycles. Additional cycles may be given at the discretion of the treating clinician.
4. High-dose Ifosfamide (IFOS): 4 cycles.

Clinicians are encouraged to use local disease control measures where possible after four cycles of chemotherapy. Stem cell harvesting may be carried out in patients for whom high-dose therapy is planned but the first four chemotherapy cycles must be given according to the randomised regimen. Patients randomised to receive TC, IT or GD who have not progressed on treatment may continue to receive the randomised regimen for more than six cycles at the discretion of the treating physician. Myeloablative therapy may be given at the discretion of the treating physician after six cycles of TC, IT or GD, or after four cycles of IFOS.

Inclusion criteria:
Participant inclusion criteria as of 14/12/2018:
1. Histologically confirmed ES.
2. Disease progression (during or after completion of first line treatment) or any subsequent recurrence OR Refractory disease, defined by progression during first line treatment or within 12 weeks of its completion. Disease progression will be based on RECIST criteria. The appearance of new bone lesions on bone scan will require confirmation with cross-sectional imaging.
3. Soft tissue disease component evaluable by cross-sectional imaging (RECIST). Patients with bone disease without a measurable soft tissue component or bone marrow disease only will be eligible for the study but will not contribute to the phase II primary outcome measure.
4. Age =4 years and <50 years.
5. Patient assessed as medically fit to receive cytotoxic chemotherapy.
6. Documented negative pregnancy test for female patients of childbearing potential.
7. Patient agrees to use effective contraception during therapy and for 12 months after last trial treatment, where applicable.
8. Written informed consent from the patient and/or parent/legal guardian.

Previous participant inclusion criteria:
1. Histologically confirmed Ewing sarcoma
2. Disease recurrence after completion of first-line treatment
3. Refractory disease, defined by progression during first-line treatment or within 12 weeks of its completion
4. Soft tissue disease component evaluable by cross-sectional imaging. Patients with bone disease without a measurable soft tissue component or bone marrow disease only will be eligible for the study but will not contribute to the phase II primary outcome measure.
5. Age 2-50 years
6. Patient assessed as medically fit to receive cytotoxic chemotherapy
7. Documented negative pregnancy test for female patients of childbearing potential
8. Patient agrees to use contraception during therapy and for 12 months after last trial treatment (females) or 5 months after last trial treatment (males), where applicable
9. Written informed consent from the patient and/or the parent/legal guardian

Exclusion criteria:
Participant exclusion criteria as of 14/12/2018:
1. Bone marrow infiltration resulting in Absolute Neutrophil Count (ANC) <1.0 x 109/L or platelets <75 x 109/L.
2. Cytotoxic chemotherapy or other investigational medicinal product (IMP) within previous two weeks.
3. Myeloablative therapy within previous eight weeks.
4. Radiotherapy to target lesion within previous six weeks.
5. Pregnant or breastfeeding women.
6. Follow-up not possible due to social, geographic or psychological reasons.
7. Previous randomisation into the rEECur trial

Additional criteria for specific arms:
1. Patients with a contraindication to any IMP may be entered into the study but may not be randomised to receive an arm that contains a contraindicated IMP. They will be eligible for trial entry as long as they can be randomised between a minimum of two study arms.
2. Patients who are unable to receive one or more IMPs due to local or national funding arrangements will be eligible for trial entry as long as they can be randomised between a minimum of two study arms.
3. Patients and investigators may decline randomisation to one or more trial regimens but will be eligible for trial entry as long as they can be randomised between a minimum of two study arms.
4. Patients who have previously received one of the trial regimens off-trial may not be randomised to receive that chemotherapy regimen again. However, patients who have received cyclophosphamide during first line therapy may be randomised to receive the TC arm and patients who have had ifosfamide during first line therapy may receive the ifosfamide arm if they do not have pre-existing renal or other toxicity that would necessitate in rEECur a dose modification. There is no requirement for a minimum time between receiving first line ifosfamide and entry to rEECur.


Previous participant exclusion criteria:
1. Conventional dose cytotoxic chemotherapy or other investigational medicinal product (IMP) within previous four weeks
2. Myeloablative dose chemotherapy within previous 8 weeks
3. Radiotherapy to target lesions within previous 6 weeks
4. Pregnant or breastfeeding women
5. Follow-up not possible due to social, geographic or psychological reasons

Additional criteria for specific arms:
1. Patients who have previously received one of the randomised regimens may not be randomised to receive that chemotherapy regimen again
2. Patients with a contraindication to any IMP may be entered into the study but may not be randomised to receive an arm that contains a contraindicated IMP
3. Patients who have received cyclophosphamide during first-line therapy may be randomised to receive the TC arm
4. Patients who have had ifosfamide during first-line therapy may be randomised to receive the IFOS arm if they do not have pre-existing renal or other toxicity that would necessitate a dose modification. There is no requirement for a minimum time between receiving first-line ifosfamide and randomisation to IFOS as part of the rEECur trial.