ESR1 and neoplasm: Once the fundamentals for the use of N-[11C]methyl-choline (11C-choline) were established, Contractor et al. [22] showed that breast tumours were well visualized in 30 of 32 patients with good tumour background ratios, albeit surprisingly a poor association was found with tumour size, estrogen receptor, progesterone receptor, human epidermal growth factor receptor-2, Ki-67, and nodal status.