PTK7 is an important tumor biomarkerand a presumed driver in the development and progression of lymphoid,hepatic, and numerous other cancers.8,37,39,41 Select reports on thecross-linking of aptamers to cell-surface proteins using electrophilicand photoreactive groups exists;14,15,42,43 however, this is thefirst example of aptamer-mediated selective and efficient transferof a small molecule label. Here, PTK7 is linked to cancer.