Dual HER2 blockade in the first-line treatment of metastatic breast cancer - A retrospective population-based observational study in Danish patients.

•Patients with HER2-positive metastatic breast cancer.•Pertuzumab and trastuzumab as first-line treatment in a real-world setting.•A cohort of 291 patients; 112 with de novo disease and 179 with recurrence.•Median OS; 41.8 months and median PFS; 15.8 months.•PFS comparable with what could be expected from the related randomized trial.