Trastuzumab is a biologic therapy indicated for the treatment of human epidermal growth factor receptor 2 (HER2)-positive breast cancer and metastatic gastric cancer. Trastuzumab was originally approved as an intravenous (IV) formulation but has since been developed for subcutaneous (SC) administration for patients with HER2-positive breast cancer. Both formulations demonstrate generally comparable pharmacological and clinical profiles. Therefore, when deciding between treatment options, factors such as the route of administration, patient preference, value and cost must be considered. Studies comparing IV with SC trastuzumab indicate that each formulation offers unique advantages to patients depending on their individual needs. Concurrent with the development of SC trastuzumab, IV trastuzumab biosimilars comprise another treatment option that, in view of their reduced cost, might improve patient access and increase cost-effectiveness for healthcare providers and payers. In this review, we seek to raise awareness of the current options available for trastuzumab so that healthcare providers can optimally treat patients according to their individual situations and preferences.