SMAD3 and breast cancer: As shown in Figure 2A and Table S1 in the Supporting Information, among the top ten of putative KAT6A‐binding proteins identified in our analysis, SMAD3 was highly enriched in the KAT6A precipitate and ten peptides of SMAD3 were identified in the protein complex (peptide score >45, peptide expect <0.01). Since SMAD3 is critical for breast cancer metastasis,[26] we chose SMAD3 as a major candidate for KAT6A regulation of breast cancer metastasis.