KLK13 and breast cancer: In addition, other members of the KLK family are known to be expressed in MCF7 breast cancer cells38, including: KLK5, which cleaves PAR1 at positions R41-S42 and F43-L44; KLK6, which cleaves PAR1 at positions R41-S42, S42-F43, F43-L44, L45-R46 and R46-N47; and KLK13, which cleaves PAR1 at positions R41-S42, F43-L44, and R46-N473.