FRK and breast cancer: Recently, several small-molecule inhibitors specifically target on PTK6 have been developed to inhibit its phosphorylation and downstream signaling [47]; XMU-MP-2, a ATP-site-directed kinase inhibitor with mild cytotoxicity, exhibited a strong inhibition on the growth of breast cancer through selectively inhibiting the activity of tyrosine kinases with SRC and FRK domain [30].