NR4A1 and cancer: However, for PET imaging, several other radiotracers that specifically target cancer hallmark processes relevant for cancer development, progression, and treatment resistance have also been developed, such as [18F]fluoromisonidazole ([18F]FMISO) for imaging hypoxia [8], [18F]fluorothymidine ([18F]FLT) for imaging proliferation [9], and [18F]fluoroestradiol ([18F]FES) for imaging hormone receptor status.