The optimal sequence of anti-human epidermal growth factor receptor 2 (HER2) therapies in metastatic breast cancer (MBC) is still undetermined. Physicians must therefore make decisions based on clinical trials and their own experience for the best treatment sequence in these patients. The objective of this review is to summarize the efficacy and safety data for trastuzumab emtansine (T-DM1) in patients with MBC. Additionally, the concept of 'loss of chance for a better outcome' is investigated. It applies to patients who are not receiving the best possible treatment for their disease. Physicians should strive to offer the best possible care, although getting optimal results in each individual patient is not guaranteed. Lastly, the number of patients with MBC lost per treatment line is evaluated. We conclude that both concepts reinforce the importance of giving the most active treatments as soon as possible in the course of disease to secure the longest possible survival for HER2-positive MBC patients.
Keywords: Antineoplastic agents; HER2-positive; Loss of chance; Metastatic breast cancer; Oncologists; Trastuzumab emtansine.