Background Immunoassays remain the primary analytical method for quantification of macromolecules such as monoclonal antibodies (mAbs). For the quantification of mAbs in serum or plasma, study samples are not immediately analysed once collected, and thus the various conditions that study samples undergo must be considered to ensure that analytical stability has not been compromised.

Purpose To analyse the long term stability of the monoclonal antibody trastuzumab (Herceptin) in serum samples at -20°C.

Material and methods Blood samples (1.5 mL) were stored in K₂EDTA tubes (Becton Dickinson, USA). They were immediately sent to the laboratory, centrifuged (2 × 3000 g/5 min) and were divided into two aliquots. One aliquot was immediately analysed. The second aliquot was stored at −20°C for 2 months and then analysed. The immediately analysed samples were considered the baseline value. At the time of analysis, both samples were analysed at dilutions of 1/20 and 1/80 in duplicate to minimise pipetting errors and the intrinsic variation of the method. Serum trastuzumab concentrations were determined by enzyme linked immunosorbent assay (ELISA) using the automated analyser TRITURUS (Grifols). SPSS statistical (v.22.0.0.0) program was used for statistical analysis. Repeated measurements made from the same samples kept under different storage conditions were tested using the Wilcoxon test. A p value <0.05 was considered to be significant. The research protocol was approved by the local ethics committee of our institution.

Results Blood samples from 4 patients a with diagnosis of HER2+ breast cancer receiving treatment with subcutaneus trastuzumab (Herceptin) were included in the study after providing written informed consent. We did not find a significant difference between the samples analysed immediately and those stored at -20°C for 60 days (p = 0.414) (table 1).

Conclusion In our study, we observed that serum trastuzumab (Herceptin) samples stored at -20°C were stable for at least 2 months. This was consistent with previous studies.

References and/or Acknowledgements

1. Ficha Técnica Herceptin

References and/or AcknowledgementsNo conflict of interest.