SB3 is a biosimilar of trastuzumab that has been approved for use in the treatment of human epidermal growth factor 2-positive breast cancer and human epidermal growth factor 2-positive gastric cancer. Antibody-dependent cellular cytotoxicity is one of several critical quality attributes of trastuzumab. Data from the development of SB3 support the hypothesis of a relationship between antibody-dependent cellular cytotoxicity activity and clinical outcomes in terms of the response rate and long-term survival. Current analytic methods utilizing advanced technology allow the detection of small changes in other quality attributes that influence antibody-dependent cellular cytotoxicity, such as glycosylation and FcγRIIIa binding. Use of such methods to monitor batch-to-batch consistency enables production of trastuzumab biosimilars with consistent quality. Trastuzumab biosimilars such as SB3 therefore have the potential to increase accessibility to trastuzumab-based therapy without compromising efficacy or safety.