SPP1 and cancer: For example, a set of 10 potential BCa serum biomarkers and cancer antigens (haptoglobin, osteopontin (OPN), CA15-3, CA125, carbohydrate antigen 19-9 (CA19-9), CEA, prolactin, α-fetoprotein (AFP), leptin, and migration inhibitory factor (MIF)) were developed for diagnosis and screening, but none of them are detected to have a high specificity, particularly in detecting early stage disease [176,177].