Trastuzumab Emtansine in Treatment of Residual Breast Cancer After Neoadjuvant Therapy: Who Will Benefit?
Chau T. Dang, MD
Pedram Razavi, MD, PhD
Sarat Chandarlapaty, MD, PhD
Shanu Modi, MD
The discovery of trastuzumab has been revolutionary in the treatment of HER2-positive breast cancer, both in the metastatic and early-stage settings.1-6 This cannot be disputed. In the early-stage setting, the addition of trastuzumab to standard chemotherapy has led to a 50% gain in disease-free survival and a 30% improvement in overall survival.3-5 Subsequently, trials enrolling patients deemed to have high-risk HER2-positive breast cancer demonstrated that extended therapy with neratinib (tyrosine kinase inhibitor against HER1/HER2/HER4) given sequentially after adjuvant trastuzumab, or the combination of pertuzumab given concurrently with trastuzumab, led to small incremental gains, particularly in patients with hormone receptor–positive cancer and node-positive disease, respectively.7,8 However, the magnitude of benefit was not nearly as significant as that observed with trastuzumab in the initial trials, until the release of KATHERINE.9
On May 3, 2019, the U.S. Food and Drug Administration approved ado-trastuzumab emtansine (Kadcyla) for the adjuvant treatment of patients with HER2-positive early breast cancer who have residual invasive disease after neoadjuvant taxane- and trastuzumab-based treatment. Approval was based on results of the KATHERINE trial.
In this randomized study, reviewed in this issue of The ASCO Post, patients with residual disease after neoadjuvant chemotherapy were randomly assigned to adjuvant trastuzumab emtansine (T-DM1) or trastuzumab alone, both for 14 cycles. T-DM1 is an antibody-drug conjugate where the antibody is trastuzumab covalently linked to the cytotoxic agent DM1. Patients who received T-DM1 achieved a 50% improvement in 3-year invasive disease–free survival over those who received trastuzumab alone (77.0% vs 88.3%, hazard ratio = 0.50, 95% confidence interval = 0.39–0.64, P < .001). This is particularly striking, given only 71.4% of patients completed all 14 cycles of T-DM1.
Based on these results, T-DM1 is considered a new standard treatment for those with residual disease after neoadjuvant chemotherapy. The results of KATHERINE echo those of the CREATE-X trial. In the CREATE-X trial, patients with HER2-negative breast cancer who had residual disease after standard neoadjuvant chemotherapy were randomly assigned to capecitabine or not; the study revealed a significant benefit in favor of more chemotherapy.10
Who Benefits From T-DM1?
Results from the KATHERINE trial raise some interesting questions: Should all patients with HER2-positive early-stage breast cancer receive neoadjuvant chemotherapy or adjuvant T-DM1 if residual disease is found? If patients are unable to complete T-DM1, should they be given standard trastuzumab alone (as per KATHERINE) or trastuzumab/pertuzumab? Although the 3-year invasive disease–free survival of 88.3% is good with T-DM1, is it good enough, or is there room for improvement?
T-DM1 is considered a new standard treatment for those with residual disease after neoadjuvant chemotherapy. The results of KATHERINE echo those of the CREATE-X trial.— Chau T. Dang, MD, and colleagues
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To answer these questions, we have to look first at our current standard-of-care approach, which is to deliver neoadjuvant therapy to those with clinical stages II to III HER2-positive breast cancer (tumor size > 2 cm, node-positive, locally advanced, or inflammatory breast cancer), where there is an impact in downstaging the breast and/or axilla. In the modern era, if pertuzumab is available, when combined with standard trastuzumab, the chance of achieving pathologic complete response is about 60%, as seen in studies such as TRYPHAENA and BERENICE.11,12
So, for patients with stage I HER2-positive breast cancer and candidates for breast conservation, delivering neoadjuvant chemotherapy has limited value and is unlikely to change the planned surgery. Moreover, updated results from the APT trial, an adjuvant study comprising largely patients with stage I HER2-positive breast cancer, demonstrated an impressive 7-year disease-free survival of 93% with paclitaxel/trastuzumab therapy.6 As such, it is highly unlikely that further adjuvant treatment with T-DM1 would offer substantial improvement to these already excellent outcomes, particularly given the risk of additional neurotoxicity, as reported in KATHERINE.9
Who Benefits From Pertuzumab?
As for those who cannot complete 14 cycles of adjuvant T-DM1, if pertuzumab is available, it is reasonable to complete 1 year of anti-HER2 therapy with the trastuzumab/pertuzumab combination. Although T-DM1 is now a new standard in those with residual disease, we still do not have direct evidence that T-DM1 is superior to trastuzumab/pertuzumab. In fact, it is noteworthy to mention that trastuzumab/pertuzumab has generally been superior to control, but T-DM1–based treatment has not in some studies.13-15 In APHINITY, although the addition of pertuzumab to trastuzumab led to a modest gain in 3-year invasive disease–free survival in the intention-to-treat population, it was more significant in those with node-positive disease in the preplanned analysis.8
When patients are unable to complete T-DM1, completing adjuvant therapy with trastuzumab/pertuzumab in those with high-risk breast cancer…is justifiable.— Chau T. Dang, MD, and colleagues
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So, it appears that the addition of pertuzumab is beneficial in those with a high burden of disease, such as those with metastatic disease and node-positive early-stage cancer. Thus, when patients are unable to complete T-DM1, completing adjuvant therapy with trastuzumab/pertuzumab in those with high-risk breast cancer, such as those with a high burden of disease (ie, node-positive),
Future Treatment Possibilities
Finally, as we look to the future and improving upon the advances we’ve already made, perhaps there will be a role for other novel agents in these high-risk patients with residual disease, such as immunotherapy and other next-generation therapies (ie, selective tyrosine kinase inhibitors, cyclin-dependent kinase 4/6 inhibitors, and other potent antibody-drug conjugates). An even more innovative approach would be to evaluate T-DM1 and/or other novel agents in patients based on circulating tumor DNA after neoadjuvant chemotherapy, including patients with conventionally determined pathologic complete response, as a subset of these patients are still at risk for distant recurrence. ■
Dr. Dang is a medical oncologist practicing at Memorial Sloan Kettering Cancer Center (MSK), New York, New York. Dr. Razavi is a medical oncologist and Instructor in Medicine at MSK. Dr. Chandarlapaty is Assistant Attending Physician and Laboratory Head, Human Oncology and Pathogenesis Program at MSK. Dr. Modi is a medical oncologist practicing at MSK.
DISCLOSURE: Dr. Dang has received institutional research funding from Genentech/Roche and Puma Biotechnology; and is a consultant/advisor for Roche/Genentech, Puma, and Daiichi Sankyo. Dr. Razavi has received institutional research funding from GRAIL and Illumina Dr. Chandarlapaty is a consultant/advisor for Sermonix Pharmaceuticals, Novartis, Context Therapeutics, Lilly, Revolution Medicine, and BMS; has received institutional research funding from Novartis, Daiichi Sankyo, Sanofi, Lilly, and Genentech; and travel/accommodations/expenses from Novartis, Sun Pharma, and BMS. Dr. Modi is a consultant/advisor for Daiichi Sankyo; is on the speakers bureau for Genentech; and has received funding from Roche/Genentech, Novartis, Seattle Genetics, Synta, and Daiichi Sankyo.
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Adjuvant Trastuzumab Emtansine vs Standard Trastuzumab in Residual HER2-Positive Breast Cancer After Neoadjuvant Therapy
In the phase III KATHERINE trial reported in The New England Journal of Medicine,1Gunter von Minckwitz, MD, of the German Breast Group, Neu-Isenburg, and colleagues found that adjuvant treatment with the antibody-drug conjugate trastuzumab emtansine (T-DM1) improved invasive disease–free survival...