The resulting, highly affine aptamers were capable ofnot only selective binding to the CCRF-CEM target cells, but also of recognizingthese cells in a mixture containing other cancer cell lines and cells from themedullary fluid of healthy individuals [27].It turned out that the 88-nt sgc8  aptamer with the highest affinity tothe target cells ( Kd  = 0.8 nM) binds to protein tyrosine kinase 7 (PTK7) on its surface[28]. Here, PTK7 is linked to cancer.