To evaluate PEAK1 expression in patient samples at the protein level, we selected four breast cancer tissue samples (two with low PEAK1 levels and two with elevated PEAK1 levels) from the Human Cancer Atlas for comparing PEAK1 IHC staining patterns with those of epithelial or mesenchymal markers that have been previously reported to be regulated by PEAK1 overexpression [21,27]. This evidence concerns the gene PEAK1 and cancer.