Maintenance Oral Etoposide or Observation Following High-dose Chemo for GCT

Inclusion Criteria:

1. Written informed consent and HIPAA authorization for release of personal healthinformation

2. Age ≥ 18 years at the time of consent

3. Histological or serological evidence of non-seminomatous GCT

4. Relapsed disease after first-line cisplatin-based combination chemotherapy

5. Completed salvage treatment with HDCT and PBSCT for 2 tandem cycles perInstitutional Guidelines

6. HDCT must have been used as the initial salvage chemotherapy regimen (2nd linetherapy) 6.1. Note: 1 or 2 cycles of standard course regimens prior to HDCT areacceptable (regimens include VeIP [vinblastine+ifosfmaide+cisplatin] or TIP [paclitaxel+ifosfamide+cisplatin] or PVB [cisplatin+vinblastine+bleomycin]

7. Normal or declining tumor markers (AFP and hCG) at time of screening

8. Adverse events from prior therapy recovered to CTCAE v5.0 grade ≤ 2 at time ofregistration

9. Women with ovarian germ cell tumors are eligible

10. Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2 within 28days of study registration

11. Last dose of HDCT must be ≤16 weeks from study registration

12. Adequate organ function lab values obtained within 28 days prior to studyregistration System Laboratory Value Hematological Absolute neutrophil count (ANC) ≥1,000 /mcL Platelets ≥100,000 / mcL Hemoglobin ≥8 g/dL Renal Serum creatinine <2mg/dL Hepatic Serum total bilirubin ≤ 1.5 X ULN OR Direct bilirubin ≤ ULN forsubjects with total bilirubin levels > 1.5 ULN AST (SGOT) and ALT (SGPT) ≤ 2.5 X ULN OR

• 5 X ULN for subjects with liver metastases Coagulation International NormalizedRatio (INR) or Prothrombin Time (PT) ≤1.5 X ULN unless subject is receivinganticoagulant therapy as long as PT or PTT is within therapeutic range ofintended use of anticoagulants Activated Partial Thromboplastin Time (aPTT) ≤1.5 X ULN unless subject is receiving anticoagulant therapy as long as PT orPTT is within therapeutic range of intended use of anticoagulants

13. If a female of childbearing potential, a negative urine pregnancy test within 28days prior to receiving the first dose of study drug. o Non-childbearing potential is defined as (by other than medical reasons):

• ≥ 45 years of age and has not had menses for >2 years

• Amenorrheic for < 2 years without a hysterectomy and/or oophorectomy and afollicle-stimulating hormone value in the postmenopausal range upon pre-study (screening) evaluation

• Post hysterectomy or oophorectomy. Documented hysterectomy or oophorectomy mustbe confirmed with medical records of the actual procedure or confirmed by anultrasound.

14. For female patients of childbearing potential and male patients with partners ofchildbearing potential, agreement (by patient and/or partner) to use two forms ofhighly effective contraception (i.e., one that results in a low failure rate [< 1%per year] when used consistently and correctly) starting with the first dose ofstudy therapy and to continue its use for 30 days after the last dose of studytherapy, or abstain from heterosexual activity.

Exclusion Criteria:

1. Relapsed pure seminoma

2. Rising tumor markers (AFP and hCG) at time of screening

3. Patients who completed 2nd cycle of HDCT (time since last dose of HDCT) >16 weeksago

4. Treatment with any investigational agent within 28 days prior to study registration

5. Other active malignancy requiring treatment in past 12 months

6. History of psychiatric illness or social situations that would limit compliance withstudy requirements

7. Active infection requiring systemic therapy

8. Previous hypersensitivity to etoposide which did not recover with supportive care

9. Pregnancy, lactation, or breastfeeding

10. Has a history or current evidence of any condition, therapy, or laboratoryabnormality that might confound the results of the trial, interfere with thesubject's participation for the full duration of the trial, or is not in the bestinterest of the subject to participate, in the opinion of the treating investigator.