Background: The epidermal growth factor receptor (EGFR) plays a role in triple-negative (estrogen receptor-, progesterone receptor-, HER2-negative) breast cancer (TNBC). This randomized, phase II study investigated the combination of the EGFR monoclonal antibody cetuximab and cisplatin in the treatment of metastatic (m) TNBC. Methods: Patients (pts) with mTNBC who had received ≥1 prior chemotherapy regimen for metastatic disease, were randomized 2:1 to treatment with either: cetuximab (400 mg/m2 initial dose then 250 mg/m2 weekly) + ≥6x 3-weekly cycles of cisplatin (75 mg/m2, d1); or ≥6x 3-weekly cycles of cisplatin alone. In the cisplatin arm, pts with disease progression (PD) during the 6 cisplatin cycles could switch to cetuximab plus cisplatin and those with PD after the 6 cycles could receive cetuximab alone. The primary endpoint was best overall response. Simultaneous null hypotheses assumed that the overall response rate (ORR) in the combination arm was ≥20% and that the ORRs were equal in both arms. Secondary endpoints included progression-free survival (PFS), overall survival (OS) and safety. All statistical tests were performed at alpha-level 0.1 Results: 173 pts were included in the intention-to-treat population: 115 were randomized to cetuximab/cisplatin and 58 to cisplatin. The cetuximab/cisplatin and cisplatin arms were well balanced for patient and disease characteristics (randomization strata, 73% first and 27% second line in both arms). Differences included: age ≥65 years (19.1% vs 12.1%) and lung metastases (55.7% vs 44.8%). 30 pts receiving cisplatin alone switched to cetuximab/cisplatin after first PD. 79.6% of patients on cetuximab/cisplatin and 73.7% on cisplatin received ≥90% of the relative dose intensity of cisplatin. Adverse events (AEs) were manageable and in line with what was expected from the different agents (grade 3/4 AEs are shown in the Table). Grade 3/4 AEs (%) Adding cetuximab to cisplatin nearly doubled the ORR: 20.0% (95% CI 13.1%, 28.5%) vs 10.3% (95% CI 3.9%, 21.2%) (p=0.5 for testing ORR against 20.0%), with an odds ratio of 2.126 (90% CI 0.945, 4.786, p=0.11). Cetuximab/cisplatin was associated with a significant 32.5% reduction in the risk of disease progression compared with cisplatin alone HR 0.675 (95% CI 0.470, 0.969, p=0.032). Median PFS times were 3.7 and 1.5 months, respectively. The benefits of cetuximab/cisplatin over cisplatin on ORR and PFS were observed consistently across sub-groups (according to patient, disease and treatment characteristics), but sample sizes were small. OS results will be presented at the meeting. Conclusions: Adding cetuximab to cisplatin increased the ORR compared with cisplatin alone and significantly improved PFS in mTNBC. Safety was manageable. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr PD01-01.