ERBB2 and neoplasm: Moreover, in heavily pretreated patients with HR-positive/HER2-positive MBC, the combination of tucatinib with letrozole and palbociclib showed a considerable anti-tumor activity with median PFS of 8.7 months (10.1 months for patients without brain metastasis and 6.0 months for those with brain metastasis) (15), and the central nervous system metastases PFS was 8 months in patients with untreated asymptomatic or treated stable patients with brain metastases (16).