Participants will undergo radiographic assessment (computed tomography or magnetic resonance imaging) of disease status every 6 weeks (± 3 days), until there is radiographic documentation of progressive disease (PD). Chemotherapy will continue for a maximum of six cycles in each arm (Or until there is radiographic documentation of PD, toxicity requiring cessation, protocol noncompliance or withdrawal of consent); participants in Arm A only will continue to receive necitumumab until there is radiographic documentation of PD, toxicity requiring cessation, protocol noncompliance, or withdrawal of consent.