A phase I study of lapatinib with whole brain radiotherapy in patients with Human Epidermal Growth Factor Receptor 2 (HER2)-positive breast cancer brain metastases.

Brain metastases are common in patients with advanced, Human Epidermal Growth Factor Receptor 2 (HER2)-positive breast cancer. We evaluated the maximum tolerated dose (MTD) and feasibility of lapatinib given concurrently with whole brain radiotherapy (WBRT). Eligible patients had (HER2)-positive breast cancer and ≥1 brain metastasis. Patients received lapatinib 750 mg twice on day one followed by 1000, 1250, or 1500 mg once daily. WBRT (37.5 Gy, 15 fractions) began 1-8 days after starting lapatinib. Lapatinib was continued through WBRT. Following WBRT, patients received trastuzumab 2 mg/kg weekly and lapatinib 1000 mg once daily. The regimen would be considered feasible if <3/27 pts treated at the MTD experienced a dose-limiting toxicity (DLT). Thirty-five patients were enrolled; 17 % had central nervous disease (CNS) only. During dose escalation, no patients receiving 1,000 or 1,250 mg and two of five patients receiving 1,500 mg experienced DLTs (grade 3 mucositis and rash). Overall, 7/27 patients at 1,250 mg (MTD) had DLTs: grade 3 rash (n = 2), diarrhea (n = 2), hypoxia (n = 1), and grade 4 pulmonary embolus (n = 2). Among 28 evaluable patients, the CNS objective response rate (ORR) was 79 % [95% confidence interval (CI) 59-92 %] by pre-specified volumetric criteria; 46 % remained progression-free (CNS or non-CNS) at 6 months. The study did not meet the pre-defined criteria for feasibility because of toxicity, although the relationship between study treatment and some DLTs was uncertain. Given the high ORR, concurrent lapatinib-WBRT could still be considered for future study with careful safety monitoring.