Genes including metallothionein-2 (Mt2) [29,30], transmembrane glycoprotein nonmetastatic B (Gpnmb) [31], caveolin 1 (Cav1) [32], Col6A1 [26,27], HLA-DR antigens-associated invariant chain (Cd74) [33,34], secretory leukocyte peptidase inhibitor (SLPI) [35], carbonic anhydrase (Car9), amphiregulin (Areg) [36–38], and peripheral myelin protein 22 (PMP22) [39] have previously been reported in association with invasive and/or metastatic phenotypes or as markers for poor prognosis in human breast cancer. Here, SLPI is linked to breast cancer.