101 Background: Clinical trials have demonstrated the benefits of trastuzumab in treating HER2EBC. However, in routine care it is unclear which patients are recommended treatment, what chemotherapy partners are used and whether patients receive all of their intended treatments. In this study we describe the real world treatment patterns in HER2EBC patients. Methods: We undertook a clinical audit of patients diagnosed with HER2EBC (stage I-III) at four Sydney-based cancer centres between 2008 and 2011. We identified patients from pathology records and extracted information on patient and cancer characteristics, treatments planned and received from medical notes and medication charts. Results: 203 patients formed the study cohort; median age 55 years (range: 21-91), all but one patient was female. 77 patients had stage I disease, 84 stage II, and 42 stage III. 176 patients (86.7%) were recommended trastuzumab-based treatment and 168 patients initiated therapy. 96 were treated with anthracycline-based chemotherapy and 70 with taxane-based chemotherapy. 76.7% completed the planned number of taxane-based treatments compared with than the 60% receiving anthracycline-based therapies; toxicity being the main reason for not completing treatment. Younger patients (OR 0.89, 95%CI 0.84-0.93, p<0.001) and those with grade 3 tumours compared to grade 1 and 2 combined (OR 3.99, 95%CI 1.31-12.08, p0.014) were more likely to be recommended trastuzumab-based treatment. Younger patients (OR 0.85, 95%CI 0.81-0.90, p <0.001) with a high HER2 gene copy number (OR 4.10, 95%CI 1.06-15.81, p 0.041) multifocal disease (OR 3.53, 95%CI 1.06- 15.82 p 0.023) and stage II and III disease (OR 0.73, 95%CI 0.25-0.90 p 0.011) were more likely to be recommended anthracycline over taxane-based therapy. Conclusions: Trastuzumab-based therapy is standard of care for patients with HER2EBC regardless of patient or cancer characteristics. Whilst chemotherapy partners are determined by patient and cancer characteristics, treatment limiting toxicities also need to be considered in order to maximise patient benefit.