Quantitative assessment of human serum transferrin receptor in breast cancer patients pre- and post-chemotherapy using peptide immunoaffinity enrichment coupled with targeted proteomics

•LC-MS/MS–based targeted proteomics coupled with SISCAPA was used for sTfR detection.•SISCAPA was effective in surrogate peptide enrichment and sensitivity enhancement.•Pre- and post-chemotherapy serum samples from breast cancer patients were analyzed.•The SISCAPA-targeted proteomics assay was compared to the ELISA method.•SISCAPA-targeted proteomics may improve the quantification of low-abundant proteins.