Safety and efficacy of gemcitabine and trastuzumab in HER2-directed therapy pretreated patients with HER2-positive metastatic breast cancer: SBP-01 study.

Abstract

142 Background: Prognosis of HER2-positive metastatic breast cancer (MBC) has been dramatically improved by trastuzumab (Tmab). More recently, newer anti-HER2 agents such as lapatinib, pertuzumab and T-DM1 have prolonged survival. Despite the efficacy of these drugs, most patients develop progressive disease during or after treatment, and alternative anti-HER2 agents plus chemotherapies are required in subsequent lines of treatment. However, there are few evidence on efficacy of Tmab-containing regimens after disease progression. Gemcitabine (GEM) is non-cross resistant to anthracycline and taxane. Preclinical studies have shown that the combination of Tmab and GEM has synergistic effect against HER2-positive breast cancer cell lines. SBP-01 study assessed the efficacy and safety of the combination of Tamb and GEM in patients with HER2-positive MBC previously treated with anti-HER2 therapy. Methods: SBP-01 study included patients treated with one or more anti-HER2 directed regimens for MBC. Patients were administered with GEM 1250 mg/m2 on days 1 and 8 of each 21-day cycle and Tmab 4mg/kg loading dose and then 2mg/kg weekly. The primary endpoint was objective response rate (ORR). Secondary endpoints included progression free survival (PFS), overall survival, and safety. Results: Between June 2011 and June 2014, 35 patients were enrolled. Patients had ER positive tumor (37.1%), a median of 2 metastatic organ sites, visceral metastasis (80.0%), prior (neo) adjuvant Tmab (22.9%) and a median of 2 prior chemotherapy regimens for MBC. Previous HER2-directed drugs included Tmab (94.3%), lapatinib (37.1%), T-DM1 (8.6%) and pertuzumab (2.9%). ORR was 22.9% (95% CI, 8.6%-36.8%). Median PFS was 146 days. Patients with stable disease response received a median of 7 cycles (6-28 cycles) of treatment. Grade3/4 leukopenia (20.0%) and neutropenia (48.6%) were observed. All non-hematological toxicities were less than grade3. Conclusions: The Combination Tmab and GEM is effective and well-tolerated regimen for patients previously treated with HER2-directed therapy, and appears to make disease stable for long time period. Clinical trial information: UMIN000005881.