SPP1 and cancer: Prior studies revealed a significant correlation between cancer detection and serum proteins such as Glypican-1 (GPC1), Carboxypeptidase A4 (CPA4), C4b-binding protein α-chain (C4BPA), plasma free amino acids (PFAA), Mucin 5AC (MUC5AC), and serum osteopontin and tissue inhibitor of metalloproteinase 1 (OPNT + TIMP-1) [42].