Mastocheck® is a breast cancer-specific diagnostic assay based on algorithmic calculations of three plasma protein markers in the blood, carbonic anhydride 1 (CA1), neural cell adhesion molecule L1-like protein (NCHL1), and apolipoprotein C-1 (APOC1), using multiple reaction monitoring (MRM)-based proteomics technique (Kim et al. 2019a; Lee et al. 2015). The gene discussed is APOC1; the disease is breast cancer.