PHASE II: Patients receive treatment as in phase I. Pertuzumab is administered at the recommended phase II dose (determined in phase I). Previously collected tumor tissue samples are analyzed for correlative studies. Samples are analyzed for KRAS mutations via polymerase chain reaction and pyrosequencing; EGFR expression via immunohistochemistry and fluorescent in situ hybridization (FISH); HER receptor and ligand gene expression; and circulating tumor cells. Additional blood samples are collected periodically to isolate circulating tumor cells and are analyzed via FISH analysis.