Expression and function of human equilibrative nucleoside transporter (hENT)-1, hENT2, and thymidine kinase 1 (TK1) were studied under normoxic and hypoxic conditions, and assessed with [<sup>18</sup>F]FLT-PET in estrogen receptor positive (ER<sup>+</sup>)-MCF7, triple-negative MDA-MB231 breast cancer (BC) cells, and MCF10A cells (human mammary epithelial cells).
Larger, prospective studies are warranted to investigate whether TK1 and sEGFR measurements may be useful for identifying healthy BRCA1/2 carriers with high risk of developing breast cancer; moreover, sEGFR measurements may serve as effective tools for assessing risk before and after BSO.