Background: Prognosis of patients (pts) failing multiple chemotherapy (CT) regimens is quite dismal. CD30 is expressed and prognostic in embryonal carcinoma, hence it is a rational target for treatment. Brentuximab Vedotin (BV) is an antibody-drug conjugate consisting of the chimeric anti-CD30 antibody SGN-30 conjugated to an antitubulin synthetic analog (MMAE). A phase 2 trial is ongoing in GCT (NCT01851200). Methods: 24 pts with biopsy-proven CD30+ GCT will receive BV 1.8 mg/Kg IV q3 weeks until disease progression or onset of unacceptable toxicity. Eligibility will include failure of 2 or 3 platinum-based CT (including HDCT). All pts will undergo measurement of serum tumor markers (STM), a computed tomography and a PET scan q6 weeks. An optimal Simon’s 2-stage design will be applied. The primary endpoint is the objective response-rate (ORR; H0: ≤ 5%, H1: ≥ 25%, α and β = 10%). In stage 1, 9 evaluable patients will be accrued. Sequential peripheral blood samples are being collected for immune profiling by flow cytometry of immune cell subsets. Results: From 07/13 to 04/15, 9 pts have been treated, 3 in third-line, and 6 beyond the third-line. 5 had received HDCT. STM decline was obtained in 7 pts (77.8%) after the first dose and in 4 pts (44.4%) after 2 doses (with normalized [1] or still positive [3] STM). ORR was 22.2% (1 CR+1 PR) according to RECIST v1.1, and there were 3 metabolic PR. 3-month PFS was 11.1% (95%CI: 0.6-38.8), 6-month OS was 85.7% (95%CI: 33.4-97.9). 1 case of reversible G3 hyperglycemia was recorded. No BV discontinuation due to toxicity occurred. In 7 evaluable pts, a trend to increasing expression of activation (HLA-DR), proliferation (Ki67), and functional differentiation (Granzyme B) markers in CD4 and CD8 T cells was observed during BV. In CR patient, an increased frequency of naive and central memory T cells was observed after the first cycle of BV, as well as a reduction in the fraction of PD1⁺/CD8⁺ T cells. Conclusions: Brentuximab is endowed with potent antitumor activity and meaningful immunomodulatory effects in GCT. The rapid development of resistance is a concern. ORR is pending confirmation in the whole sample size. Clinical trial information: NCT01851200