Trastuzumab, a humanised IgG1 monoclonal antibody used to treat HER2-overexpressing metastatic breast cancer, has been developed (from infusion initially) into a subcutaneous formulation using recombinant human hyaluronidase to enhance delivery by temporarily breaking down hyaluronan, a barrier-forming substance in the tissues beneath the skin. Approved in 2019, the subcutaneous formulation follows a fixed-dose regimen, making it easier and quicker to administer than the original intravenous version. Trastuzumab primary patents expired in 2012. Secondary patents on the subcutaneous formulation have been filed and granted widely in LMICs and are expected to expire in 2030.