Several other radiotracers have been investigated; targets and examples include: proliferation (18 F-fluorothymidine [18 F-FLT]), tumor hypoxia (64Cu-diacetyl-bisN [4]-methyl thiosemicarbazone [64Cu-ATSM] and 18 F-fluoromisonidazole [18 F-FMISO], angiogenesis (Arg-Gly- Asp (R-G-D) based radiotracers targeting integrin αvβ3 which is associated with angiogenesis [18 F-RGD]) and tumor endocrine receptor (ER) expression (the estrogen receptor with 16α-18 F-fluoroestradiol [18 F-FES]). Here, ESR1 is linked to neoplasm.