Approximately 260,000 women will be diagnosed with breast cancer each year in the United States alone in 2018.

Breast cancer presents with many distinct biological subtypes. For instance, overexpression of human epidermal growth factor receptor 2 (HER2), which occurs in 20% of breast cancers, warrants targeted anti-HER2 treatment with therapies such as trastuzumab, pertuzumab, lapatinib, and neratinib.

Results from the KATHERINE trial, published last month in the New England Journal of Medicine, showed that adjuvant treatment with trastuzumab emtansine (T-DM1) in patients who had residual disease after neoadjuvant chemotherapy and HER2-targeted therapy reduced the risk of recurrence of invasive breast cancer or death by 50% compared with those who continued treatment with trastuzumab.1 No new safety signals were reported during the trial.

In patients with early breast cancer, residual invasive disease after neoadjuvant chemotherapy with HER2-directed therapy is associated with a higher risk of recurrence and metastatic disease as compared to no residual disease. Therefore this subset of high-risk patients have a high unmet medical need for effective therapies in the early stages of their disease.1,2


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Neoadjuvant treatment in patients with early disease can induce tumor shrinkage and has been shown to lead to better results in the adjuvant setting in metastatic disease. In patients who have residual disease after treatment in the neoadjuvant setting, the standard of care is chemotherapy for one year followed by a minimum of 5 years of endocrine therapy.1

The pathological complete response (pathCR) rate, defined as the eradication of residual disease in the breast and the lymph nodes after drug therapy as assessed at surgery, is generally prognostic for improvement in overall and disease-free survival.2 PathCR after preoperative therapy may be used as a biomarker for treatment selection in, or clinical trial enrollment of, high-risk patients with HER2-positive early breast cancer.2

T-DM1, an antibody-drug conjugate of trastuzumab and emtansine, has shown benefit in metastatic breast cancer that was previously treated with neoadjuvant chemotherapy plus HER2-targeted therapy.1,2,3 T-DM1 retains the HER2-directed activity of trastuzumab, and delivers cytotoxic emtansine intracellularly into HER2 overexpressing cells, inducing tumor shrinkage with minimal exposure of healthy tissue.4