Relationship Between Hypoxia and Endocrine Response in Human Breast Cancer

Approximately 30% of ER-positive breast cancer will unfortunately display primary resistance to hormonal therapy, and some may develop acquired resistance to the therapy after initial treatment. Hypoxia is a normal phenomenon in solid tumors that arises, in part, from uncontrolled proliferation and immature blood vessels. Previous studies have demonstrated hypoxia significantly reduced both the growth-promoting effects of estradiol (E2) and the growth-inhibitory effects of an antiestrogen on ER-positive breast cancer cell lines. A recent study comparing neoadjuvant letrozole with letrozole plus metronomic cyclophosphamide found that increased levels of HIF-1a were significantly associated with resistance to treatment. Taken together, these data indicate that hypoxia might be associated with endocrine resistance in breast cancer. With PET/CT, radiolabeled hypoxia-avid compounds can be applied to evaluate oxygenation status in experimental or human tumors. 18F-labeled fluoromisonidazole (1-\[2-nitro- 1-imidazolyl\]-2-hydroxy-3-fluoropropane \[18F-FMISO\]) PET/CT is the most widely used one in the clinic. Studies have demonstrated an excellent correlation between the 18F-FMISO uptake and oxygenation status of several cancers including breast cancer. The major aim of our study was to analyze uptake of 18FFMISO as well as the IHC expression of HIF-1-alpha in ER-positive breast cancers, and to predict the clinical, pathological and biological response of primary endocrine therapy.