Surprisingly, aptamer was detected in each of the four treatment groups, including TENN and TENN-DOX, most likely entering the brain microenvironment through a nonspecific transport mechanism as reported in a healthy animal model (<0.025% injected dose/g tissue) [25] (Fig. 8), although given that MDA-MB-231Br cells express TfR, some accumulation of TENN-DOX in the tumor might be expected (Supplementary Data and Supplementary Fig. S1). The gene discussed is TFRC; the disease is neoplasm.