There were six proteins (kallikrein 6, ATP‐binding cassette sub‐family C member 11, secretoglobin family 3A member 1, mammaglobin‐A, prolactin‐inducible protein [PIP], and mucin‐like protein 1) that are most strongly expressed in breast tissues (compared to all other tissues), and although not cancer specific, may prove useful indicators of breast health. This evidence concerns the gene KLK6 and cancer.