Five KLKs were commonly downregulated in head-neck squamous cell carcinoma and breast invasive carcinoma: KLK3 (3-fold and 4-fold), KLK6 (2-fold and 6-fold), KLK7 (2-fold and 10-fold), KLK11 (5-fold and 6-fold) and KLK13 (8-fold and 3-fold). Here, KLK3 is linked to invasive breast carcinoma.