GNRHR and colon carcinoma: One of the first conjugates targeting different GnRH-R-positive tumor cells (e.g., ovarian, endometrial or colon carcinomas) was designed in Schally’s lab by attaching doxorubicin to the GnRH-I-[6D-Lys] superagonist via an ester bond [17,39] and approved as zoptarelin doxorubicin [53].