Adjuvant Trastuzumab Monotherapy for Older Patients with HER-2 Positive Breast Cancer

SUMMARY: Breast cancer is the most common cancer among women in the US and about 1 in 8 women (13%) will develop invasive breast cancer during their lifetime. Approximately 276,480 new cases of invasive female breast cancer will be diagnosed in 2020 and about 42,170 women will die of the disease. Approximately 15-20% of invasive breast cancers overexpress HER2/neu oncogene, which is a negative predictor of outcomes without systemic therapy. Trastuzumab is a humanized monoclonal antibody targeting HER2. Adjuvant and neoadjuvant chemotherapy given along with Trastuzumab reduces the risk of disease recurrence and death, among patients with HER2-positive, early stage as well as advanced metastatic breast cancer. Since the approval of Trastuzumab, several other HER2-targeted therapies have become available. The duration of adjuvant Trastuzumab therapy has been 12 months and this length of treatment was empirically adopted from the pivotal registration trials.

Elderly patients with HER-2 positive breast cancer may not be candidates for adjuvant chemotherapy. Single agent Trastuzumab used as adjuvant treatment without chemotherapy could be of potential benefit, avoiding chemotherapy-induced toxicities. However, the benefit of single agent Trastuzumab has not been investigated in patients older than 70 years. The present study was designed to investigate the efficacy of Trastuzumab monotherapy, compared with Trastuzumab in combination with chemotherapy, incidence of Adverse Events, as well as Quality of Life, in terms of the noninferiority criterion.

RESPECT Study is a multicenter, open-label, randomized controlled, prospective, adjuvant, noninferiority trial, in which Trastuzumab monotherapy was compared with Trastuzumab plus chemotherapy, among patients older than 70 years, with HER-2 positive breast cancer. A total of 275 patients, aged 70-80 years with surgically treated HER-2 positive invasive breast cancer, were randomly assigned in a 1:1 ratio to receive either Trastuzumab monotherapy (N=137) or Trastuzumab plus chemotherapy (N=138). Trastuzumab plus chemotherapy treatment consisted of a loading dose of Trastuzumab at 8 mg/kg and a maintenance dose of 6 mg/kg every 3 weeks for 1 year. Chemotherapy regimens consisted of either Paclitaxel 80 mg/m2 IV weekly for 12 weeks, Docetaxel 75 mg/m2 IV every 3 weeks for 4 cycles, Doxorubicin 60 mg/m2 IV and Cyclophosphamide 600 mg/m2 IV (AC) every 3 weeks for 4 cycles, Epirubicin 90 mg/m2 IV and Cyclophosphamide 600 mg/m2 IV (EC) every 3 weeks for 4 cycles, Cyclophosphamide 75-100 mg orally, Methotrexate 40 mg/m2, and 5-fluorouracil 500-600 mg/m2 IV (CMF) for 6 cycles, Docetaxel 75 mg/m2 IV and Cyclophosphamide 600 mg/m2 IV (TC) every 3 weeks for 4 cycles or Docetaxel 60-75 mg/m2 IV, Carboplatin AUC 5-6 mg/ml/min IV along with Trastuzumab IV (TCH) every 3 weeks for 6 cycles. Patients treated with Trastuzumab monotherapy received similar doses of loading and maintenance Trastuzumab. Patients were stratified based on Performance Status, Hormone Receptor status and pathologic nodal status. Approximately 44% of patients had Stage I disease, 42% had Stage IIA, 13% had IIB, and 1% had IIIA disease. Approximately 14% of patients received Selective Estrogen Receptor Modulators such as Tamoxifen, and about 69% of patients received Aromatase Inhibitors. The Primary endpoint was Disease Free Survival (DFS) with assessment of prespecified Hazard Ratio (HR) and Restricted Mean Survival Time (RMST) for each treatment group. (RMST has been advocated as an alternative or a supplement to the Hazard Ratio for reporting the effect of an intervention in a randomized clinical trial, and is a measure of average survival from time 0 to a specified time point, and may be estimated as the area under the KM curve up to that point. RMST measure is especially informative for older patient populations in which Quality of Life issues are more important). Secondary endpoints included Overall Survival (OS), Relapse-Free Survival (RFS), Adverse Events (AEs) and Health-Related Quality of Life (HRQoL). The median follow up time was 4.1 years.

The 3-year DFS was 89.5% with Trastuzumab monotherapy versus 93.8% with Trastuzumab plus chemotherapy (HR=1.36; P=0.51) and this study failed to meet the prespecified criterion for noninferiority. However, a preplanned analysis of DFS according to RMST was -0.39 months, suggesting that only 0.39 months of DFS were lost within 3 years, by avoiding chemotherapy. The 3-year RFS was 92.4% with Trastuzumab monotherapy versus 95.3% with Trastuzumab plus chemotherapy (HR=1.33) and the difference in RMST for RFS between treatment groups at 3 years was −0.41 months (P=0.53). There were significant differences noted in clinically meaningful HRQoL deterioration rate at 2 months (31% for Trastuzumab monotherapy versus 48% for Trastuzumab plus chemotherapy; P=.016) and at 1 year (19% versus 38%; P=0.009). Breast cancer-specific survival at 3 years was 99.2% with Trastuzumab monotherapy versus 99.2% with Trastuzumab plus chemotherapy (HR=0.20; P=0.14).

The authors concluded that even though the Primary endpoint of noninferiority for Trastuzumab monotherapy was not met, the Restricted Mean Survival Time revealed that the observed loss of survival without chemotherapy was less than 1 month at 3 years, and Health-Related Quality of Life was better, with lower toxicities. Therefore, Trastuzumab monotherapy can be considered as a reasonable adjuvant therapy option for a select group of elderly patients with favorable outcomes.

Randomized Controlled Trial of Trastuzumab With or Without Chemotherapy for HER2-Positive Early Breast Cancer in Older Patients. Sawaki M, Taira N, Uemura Y, et al. J Clin Oncol. 2020;38:3743-3752.