Therefore, this paper proposes two new stochastic microsensors based on carbon nanopowder (nC) modified with gold nanoparticles (AuNp) and two porphyrins—5,10,15,20-tetraphenyl-21H,23H-porphine (TPP) and 5,10,15,20-tetrakis (pentafluorophenyl chlo-ride)-21H,23H-iron (III) porphyrin (Fe(TPFPP)Cl)—for the simultaneous assay of CEA, CA15-3 and HER2, because a screening test based on their simultaneous assay will provide more information about the diagnostic and personalized treatment of breast cancer. Here, ERBB2 is linked to breast carcinoma.