Despite marked improvements in survival among patients with ERBB2+ breast cancer, CNS recurrence remains a common issue, as most drugs lack effective CNS penetration.15 Thus, an emerging problem is the increasing number of patients with CNS-limited disease, as highlighted by our study, which identified 26.6% of patients presenting with CNS-only disease at CNS metastasis diagnosis. Here, ERBB2 is linked to metastasis.