SUMMARY: Breast cancer is the most common cancer among women in the US and about 1 in 8 women (12%) will develop invasive breast cancer during their lifetime. Approximately 266,120 new cases of invasive breast cancer will be diagnosed in 2018 and about 40,920 women will die of the disease. The HER or erbB family of receptors consist of HER1, HER2, HER3 and HER4. Approximately 15-20% of invasive breast cancers overexpress HER2/neu oncogene, which is a negative predictor of outcomes without systemic therapy. HERCEPTIN® (Trastuzumab) is a humanized monoclonal antibody targeting HER2, and adjuvant and neoadjuvant chemotherapy given along with HERCEPTIN® 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 HERCEPTIN®, several other HER2-targeted therapies have become available. The duration of adjuvant HERCEPTIN® therapy has been 12 months and this length of treatment was empirically adopted from the pivotal registration trials.
KADCYLA® (Ado-Trastuzumab Emtansine, T-DM1) is an Antibody-Drug Conjugate (ADC) comprised of the antibody HERCEPTIN® and the chemotherapy agent Emtansine, linked together. Upon binding to the HER2 receptor, it not only inhibits the HER2 signaling pathways but also delivers a chemotherapy agent Emtansine, a microtubule inhibitor, directly inside the tumor cells. This agent is internalized by lysosomes and destroys the HER2-positive tumor cells upon intracellular release. In the EMILIA trial, KADCYLA® was associated with significant increase in Overall Survival when compared with TYKERB® (Lapatinib) plus XELODA® (Capecitabine), in HER2-positive metastatic breast cancer patients, who had previously received HERCEPTIN® and a Taxane.
It is well established that patients with HER2-positive early breast cancer following HERCEPTIN® based neoadjuvant therapies have a pathological Complete Response rate of 40-60%. Those without a pathological Complete Response tend to have significantly less favorable outcomes. These patients irrespective of pathological response status complete their standard adjuvant therapy which includes 12 months of HER2-targeted therapy. KATHERINE trial was conducted to evaluate the benefit of switching from standard HER2-directed therapy to single-agent KADCYLA®, after neoadjuvant chemotherapy along with either single or dual HER2 targeted therapy, in patients with residual invasive cancer at surgery. This study was conducted to address the unmet need of patients who have residual invasive breast cancer after receiving neoadjuvant chemotherapy plus HER2-targeted therapy.
The KATHERINE trial is an open-label, phase III global study, which compared KADCYLA® with HERCEPTIN®, as an adjuvant treatment for patients with HER2-positive early breast cancer, who had residual invasive disease following neoadjuvant chemotherapy and HERCEPTIN®. This study included 1,486 patients with HER2-positive early stage breast cancer, who were found to have residual invasive disease in the breast or axillary lymph nodes at surgery, following at least six cycles (16 weeks) of neoadjuvant chemotherapy with a Taxane (with or without Anthracycline) and HERCEPTIN®. Within 12 weeks of surgery, patients (N=1486) were randomly assigned in a 1:1 ratio to KADCYLA® 3.6 mg/kg IV every 3 weeks or HERCEPTIN® 6 mg/kg IV every 3 weeks, for 14 cycles (743 patients in each group). Both treatment groups were well balanced and hormone receptor positive disease was present in 72% of the patients. The majority of the patients (77%) had received an Anthracycline-containing neoadjuvant chemotherapy regimen, and in 19% of the patients, another HER2-targeted agent in addition to HERCEPTIN® (dual HER2 blockade) had been administered as a component of neoadjuvant therapy. The Primary end point was invasive Disease Free Survival (defined as freedom from ipsilateral invasive breast tumor recurrence, ipsilateral locoregional invasive breast cancer recurrence, contralateral invasive breast cancer, distant recurrence, or death from any cause). The median duration of follow up was 41.4 months in the KADCYLA® group and 40.9 months in the HERCEPTIN® group.
At the prespecified interim analysis, invasive disease occurred in 12.2% of patients who received KADCYLA® and 22.2% of patients who received HERCEPTIN®. The estimated percentage of patients who were free of invasive disease at 3 years was 88.3% in the KADCYLA® group and 77.0% in the HERCEPTIN® group. Invasive Disease Free Survival, which was the Primary end point of the study, was significantly higher in the KADCYLA® group than in the HERCEPTIN® group (HR=0.50; P<0.001).This suggested that KADCYLA® reduced the risk of developing an invasive breast cancer recurrence or death by 50%. Distant recurrence as the first invasive disease event occurred in 10.5% of patients in the KADCYLA® group and in 15.9% of the HERCEPTIN® group. A consistent benefit was seen across all prespecified subgroups. Adverse events were consistent with the known safety profile of KADCYLA®, with more toxicities associated with KADCYLA® than with HERCEPTIN®. Additional follow-up will be necessary to determine the Overall Survival benefit with adjuvant KADCYLA®.
It was concluded that among patients with HER2-positive early breast cancer who had residual invasive disease after completion of neoadjuvant therapy, substituting KADCYLA® for adjuvant HERCEPTIN® reduced the risk of recurrence of invasive breast cancer or death by 50%, with the benefit seen across all patient subgroups. The authors added that even though KATHERINE trial focused on higher-risk patients with residual invasive breast cancer after completion of neoadjuvant chemotherapy, CNS recurrence remains a persistent problem. Trastuzumab Emtansine for Residual Invasive HER2-Positive Breast Cancer. von Minckwitz G, Huang C-S, Mano MS, et al. for the KATHERINE Investigators. (published online December 5, 2018). N Engl J Med 2019;380:617-628
