Background and importance Pertuzumab is indicated for use in combination with trastuzumab and docetaxel in adult patients with HER2-positive metastatic or locally recurrent unresectable breast cancer, who have not received previous anti-HER2 therapy or chemotherapy for their metastatic disease. The first biosimilars of trastuzumab were marketed in 2018. Biosimilar medicines are safe and effective, provide a lower cost treatment option for the national health service, and therefore allow increased access to high-cost therapies.

Aim and objectives Cost-effectiveness comparison of pertuzumab+trastuzumab originator versus pertuzumab+trastuzumab biosimilar. Evaluation of the efficacy and safety of treatment with biosimilar trastuzumab and economic impact.

Material and methods Retrospective observational study. Data of the number of patients, treatment cycles and association prescribed were extrapolated from the consultation of prescriptions entered on the drug regulatory agency’s monitoring register platform. Monitoring registers platform is an IT system that allows access to treatment in a homogeneous manner throughout the country.

These are instruments that allow the control of the prescriptive appropriateness and are an administrative control modality.

Results In our hospital since 2014, 30 patients have been treated. There are 11 active treatments; 3 patients have started treatment directly with biosimilar trastuzumab. Of the 19 closed treatments more than 84% ended before the switch to biosimilar trastuzumab took place. For the 11 currently active treatments, the average number of cycles per patient is 80. The number of treatments performed to date with trastuzumab biosimilar-pertuzumab combination has been 464. Each cycle of biosimilar trastuzumab has an average cost of €315. Each cycle of originator trastuzumab had an average cost of €1011. The switch to biosimilar trastuzumab has resulted in a saving of about €323 000.

Conclusion and relevance In clinical practice, treatment in combination with biosimilar trastuzumab has demonstrated efficacy and safety, with no increase in end-of-treatment for progression/toxicity/causes dependent on the biosimilar drug. The reduction in economic impact was significant.

Conflict of interest No conflict of interest