ASCO 2018: highlights in HER2-positive metastatic breast cancer

At the 2018 ASCO Annual Meeting, data from several interesting studies in HER2-positive metastatic breast cancer were presented. While not immediately practice changing, these trials indicate the future directions of drug development in this field. Early phase studies with novel antibody-drug conjugates (ADCs) such as trastuzumab-deruxtecan and trastuzumab-duocarmazine suggest relevant clinical activity of these drugs in pretreated patients; in addition, these ADCs may offer activity in low HER2-expressing tumours as well. ZW25, a bispecific HER2-directed antibody targeting the extracellular domains 2 and 4, showed excellent tolerability and considerable single-agent activity. A combination of T‑DM1 with the tyrosine-kinase inhibitor neratinib yielded high response rates, while a study of trastuzumab plus durvalumab reported disappointing results. Although formally negative, overall survival data from the PHEREXA trial suggest clinical activity of dual HER2-inhibition with trastuzumab and pertuzumab in patients with prior trastuzumab treatment for advanced disease. A combined analysis of two tucatinib studies showed that systemic therapy is active when continued in case of isolated central nervous system progression and stable extracranial disease after local therapy of brain metastases; finally, a small prospective observation in asymptomatic patients with reduced left ventricular ejection fraction suggests that anti-HER2 treatment may be reasonably safe in this population.