e18387 Background: The subcutaneous presentation of trastuzumab has been recently incorporated into the treatment regimen of HER2-positive breast cancer (BC). Its use has been associated with cost savings and reduced chair time, being especially suitable for public health systems. Aim: To estimate the cost savings of the use of SC-T compared to intravenous trastuzumab (IV-T) according to patient weight, and calculate the infusion time of SC-T in a tertiary healthcare facility at TecSalud from Feb 2018 - Jan 2019. Methods: From a total of 2068 oncological treatments, 756 corresponded to SC-T, either alone or concomitantly with chemotherapy (CT). For cost estimation, we considered $1,103 USD per SC-T vial, $1,162 USD per IV-T vial and $2.6 USD per mg of IV-T, as per governmental rates. We compared the actual treatment cost of 600 mg fixed SC-T dose with the hypothetical cost of administering IV-T at a dose of 6 mg/kg, considering its price per vial and per mg. The total time of SC-T infusion was reported. Results: Median patient weight for the 756 reported SC-T treatments was 72 kg (45 - 127 kg). Of these, 561 consisted of SC-T alone; and 56% had adjuvant, 34% neoadjuvant and 10% palliative intent. The estimated cost of the 756 doses of SC-T was $833,500 USD. Considering patients’ weight, 46% of the infusion treatments would have required 2 IV-T vials, with a total of 1105 vials and an absolute cost of $1,282,374 USD. Likewise, if cost per mg of IV-T is examined, we would have used 338,744 mg of IV-T, with an estimated cost of $894,284 USD. Approximate savings of SC-T use would reach $448,874 USD per vial payment and $60,784 USD per mg payment. The median time of SC-T only infusion was of 3 minutes (1 - 20 minutes); and no adverse effects were documented during its administration. Conclusions: The SC-T fixed dose (irrespectively of patients’ weight) results in significant practical and financial advantages as weight-adjusted dosing is not required. This is specially relevant in countries like Mexico, where > 70% of BC patients are overweight/obese, requiring higher doses of IV-T and resulting in greater expenses. Thus, the use of SC-T not only offers greater convenience to patients, but also reduces overall healthcare costs compared to standard IV infusion.