INTRODUCTION: The subcutaneous (H-SC) formulation of trastuzumab was demonstrated to be as effective and safe as intravenous (H-IV) and highly preferred by patients in early breast cancer. The present randomized MetaspHER trial (NCT01810393) has been the first study assessing patient's preference in metastatic setting and we report the final analysis with long term follow-up. METHODS: Patients with HER2-positive metastatic breast cancer who completed a first line chemotherapy with trastuzumab and achieved a long terms response lasting more than 3 years were randomized to receive 3 cycles of 600 mg fixed-dose H-SC, followed by 3 cycles of standard H-IV, or the reverse sequence. The primary endpoint was overall preference for H-SC or H-IV at cycle 6 and was previously reported. Secondary endpoints included safety over 1 year of treatment and with 4 additional years follow up. Overall survival (OS) and progression free survival (PFS) were assessed in this final analysis. RESULTS: A total of 113 patients were randomized and treated and the median follow-up duration was 45.4 months (range: 0.8-48.8). After the cross over period all patients excepted 2 pursued the H-SC. During the 18 cycles overall treatment period, at least 1 adverse event (AE), 1 AE of grade ≥3, and 1 serious adverse events (SAE) were respectively reported among 104 patients (92.0%), 23 patients (20.4%), and 16 patients (14.2%), respectively. Also, 10 patients (8.9%) experienced at least 1 cardiac event, including 4 patients (3.5%) with ejection fraction decreased. Beyond cycle 18 no significant additional safety concern emerged. PFS and OS rates at months 42 were 74.8% (64.7%-82.4%) and 94.9% (88.2%-97.9%), respectively. No factor appeared related to the survival outcome excepted the complete response status at baseline. CONCLUSION: The safety was consistent with the known H-IV and H-SC profiles without any safety concern raised over a prolonged exposure to H-SC.