Despite the widespread use of trastuzumab in the management of patients with HER2-overexpressing metastatic breast cancer, its optimal duration of administration is unknown. We retrospectively reviewed the medical records of 80 such patients who received trastuzumab monotherapy or combination chemotherapy beyond disease progression in order to register their clinical course. Median age of the patients was 54 years. Ninety-one percent had 3+ HER2 overexpression and 9% had 2+ HER2 overexpression. Fifty-six percent of patients had previously been treated with chemotherapy for advanced disease. The most commonly used combinations in first- and second-line treatments were trastuzumab with paclitaxel and trastuzumab with vinorelbine, respectively. In total, 32 responses were observed, most of them during the second or third line of treatment. Severe toxicities frequently seen (in = 5% of patients) were neutropenia (25%), thrombocytopenia (11.5%), infection (10%), peripheral neuropathy (9%), nausea/vomiting (6%), stomatitis (6%), diarrhea (6%), constipation (6%), edema (6%), and myalgias/arthralgias (5%). Median survival from diagnosis of advanced disease was 43.4 months (range, 6.4-91.7+), whereas median survival from disease progression after trastuzumab administration was 22.2 months (range, 0.01-32.9+). In conclusion, this retrospective analysis suggests that continuation of trastuzumab beyond disease progression in patients with HER2-overexpressing metastatic breast cancer is feasible and safe. Randomized studies are warranted.