De-escalation Study for Stage IIa/IIb < 3 cm Seminoma

Inclusion criteria : 1. Age ≥ 18 years on the day of signing informed consent. 2. Primary testicular seminomatous germ cell tumor. 3. Stage IIa/IIb \< 3 cm in largest diameter seminoma, histologically proved after orchiectomy. 4. Confirmation of a progressive disease (positive PET scan or increase of lymph nodes size by two successive CT scan). 5. Good prognosis according to IGCCCG and LDH \< 2.5 x Upper Limit of Normal (ULN). 6. Normal alpha-fetoprotein (AFP) before and after orchiectomy. 7. No prior treatment with radiotherapy or chemotherapy. 8. Eastern Cooperative Oncology Group (ECOG) Performance Status (PS) ≤ 2. 9. Adequate bone-marrow, hepatic, and renal functions with: * Neutrophils ≥ 1.5 x Giga/l, platelets ≥ 100 x Giga/l, * Aspartate aminotransferase (AST) and Alanine aminotransferase (ALT) ≤ 1,5 x ULN, * Serum creatinine \< 140 µmol/l OR calculated clearance \> 60 ml/min (using either Cockcroft-Gault formula or Modification of Diet in Renal Disease (MDRD) for \> 65 years old), * Total bilirubin ≤ ULN (if \> ULN, direct bilirubin ≤ ULN). 10. Willingness and ability to comply with scheduled visits, treatment plans, laboratory tests, and other study procedures. 11. Accepting to use effective contraceptive measures or abstain from heterosexual activity, for the course of the study and through 12 months after the last dose of chemotherapy or being surgically sterile. All patients should seek advice regarding cryoconservation of sperm prior treatment initiation because of the possibility of infertility 12. Affiliation to a health insurance. 13. Signed and dated informed consent. Non-exclusion criteria : 1. Extra-retroperitoneal metastasis on Computed tomography scan (CT scan). 2. Infection by Human Immunodeficiency Virus (HIV), or active infection with the Hepatitis B or C virus. 3. History, within 2 years, of cancer other than seminoma, except for treated skin cancer (basal cell). 4. Uncontrolled or severe cardiovascular pathology. 5. Uncontrolled or severe hepatic pathology. 6. Patient deprived of liberty or requiring tutorship or curatorship. 7. Psychological, physical, sociological, or geographical conditions that would limit compliance with study protocol requirements (at the investigator's discretion). 8. Participation to another clinical trial, except for supportive care trials.