Eligible patients will be treated with brentuximab vedotin at 1.8 mg/kg IV every 3 weeks (maximum dose of 180 mg) indefinitely until disease progression, unacceptable toxicity, or study closure.Eligible patients with grade 2 peripheral neuropathy at enrollment will be treated with brentuximab vedotin at 1.2 mg/kg IV every 3 weeks (maximum dose of 180 mg) indefinitely until disease progression, unacceptable toxicity, or study closure. Response to treatment will be assessed clinically with history, physical exam and tumor markers measurement (BHCG and AFP) on day 1 of each cycle and with CT scans after cycle 2, 4, and every 4 cycles thereafter while receiving treatment.