KLK9(kallikrein-related peptidase 9) also known as kallikrein 9 or KLK-L3, belongs to the kallikrein subgroup of serine proteases, which have diverse physiologic functions in many tissues. The KLK9 gene contains 5 coding exons and is mapped to 19q13.41. The KLK9 gene is regulated by steroid hormones in a human breast cancer cell line. Yousef et al.(2001) performed a quantitative analysis of KLK9 expression in ovarian cancer. The results indicated thatKLK9 is under steroid hormone regulation in ovarian and breast cancer cell lines. KLK9 is a potential independent favorable prognostic marker for early-stage, low-grade, optimally debulked ovarian cancer patients.