Background and Importance The ongoing rise in healthcare costs makes it necessary to establish containment strategies, in parallel with the commitment to improve access to the most effective andsafest treatments. In this sense, it is postulated that the availability of the biosimilar trastuzumab offers cost savings compared to the innovator, which could lead patients to switch drugs, maintaining efficacy while decreasing the cost of HER-2 positive breast cancer treatment.

Aim and Objectives The aim of this study was to evaluate the cost saving impact of the introduction of biosimilar trastuzumab in the treatment of HER-2 positive breast cancer in a tertiary hospital.

Material and Methods Observational, retrospective study of patients treated with biosimilar trastuzumab between January 2022 and December 2022 in a tertiary hospital.

Variables collected demographics (sex and age), number of patients, stage (early stage, locally advanced or metastatic) and economic (price of original trastuzumab and biosimilar trastuzumab).

Variables analysed economic savings, estimated number of patients who could benefit from treatment based on the savings achieved.

Results 59 patients included between January and December 2022 with a median age of 54.7+/-12.27. 42.4% (n=25) had an early stage, 23.7% (n=14) locally advanced and 33.9% (n=20) metastatic.

In our hospital, the price of one biosimilar-trastuzumab-420mg vial is €130 (0.31 €/mg) and €414.4 for 1 original-trastuzumab-150mg vial (2.76 €/mg). Treatment of our patients with biosimilar trastuzumab cost a total of €66,011.4. If these patients had been treated with the original trastuzumab, the cost would have been €587,714.4, a saving of 88.7% (€521,703).

If the average weight of a 54-year-old woman in Spain is about 70–75 kg according to the Statistics National Institute, the saving of €587,714.4 (1,895,852.9mg) would allow the 18-cycle finite treatment between 229 and 246 women with early-stage breast cancer.

Conclusion and Relevance Innovation in biological therapies, as well as the increase in candidates to receive them, has grown significantly. It is associated with an increase in costs that may become unaffordable for public Health Service. The inclusion of biosimilar drugs in breast cancer represents a significant economic saving in the treatment of breast cancer, while contributing to maintaining the sustainability of the national health system.

References and/or Acknowledgements No conflict of interest.

Conflict of Interest No conflict of interest.