As expected, the SP3 antibody recognizes a protein band of ∼185 kDa corresponding to predicted molecular weight of full-length HER2 in whole cell extracts of both human breast cancer cells (SKBR3, Figure 4A, line 1) and feline mammary tumor cells (FMCp, Figure 4A, lane 2), and cross-reacts with the recombinant human HER2-ECD (Figure 4A, lane 3, 84-90 kDa). Here, SP3 is linked to breast cancer.