We performed tandem mass spectrometry-based proteomics of secretomes and exosome-like extracellular vesicles from BRCA1-deficient and BRCA1-proficient murine breast tumor models to identify extracellular protein biomarkers, which can be used as an adjunct to current diagnostic modalities in patients with BRCA1-deficient breast cancer. The gene discussed is BRCA1; the disease is breast carcinoma.