Trial Information

Positron Emission Tomography (PET) With 18F-Fluoroestradiol (FES) as a Predictor of Response in Patients With Breast Cancer Scheduled to be Treated With MK-2206 in Combination With Either an Aromatase Inhibitor or Fulvestrant on NCI Protocol 8762

Approximately 75% of all invasive breast cancers are hormone sensitive [estrogen-receptor
positive (ER+) or progesterone-receptor positive (PR+)] and patients with such cancers are
candidates for endocrine therapy. Endocrine therapy is a central component of the treatment
of hormone-sensitive breast cancer in the adjuvant and, increasingly, neoadjuvant settings.
Knowledge of hormone receptor expression is essential for selection of appropriate therapy.
Measurement of hormone-receptor expression [estrogen receptor (ER) or progesterone receptor
(PR)] using in vitro assays of the tumor tissue at the time of primary diagnosis is standard
of clinical care. However, the presence of these hormone receptors predicts for clinical
benefit in only 30-50% of women with advanced disease receiving first-line endocrine therapy
and 15-30% receiving second-line therapy (1-3). Thus, the presence of a hormone receptor
does not indicate that the receptor is functional and essential to the growth of the cancer
cell, nor does it imply that interference with receptor function will result in tumor cell
kill. There are several shortcomings of the in vitro assays and neither quantitative nor
qualitative receptor assays performed on samples of tumor tissue completely predict the
response to antiestrogen therapy in breast cancers. In addition, none of the current
clinical tools (serologies, prognostic factors, or radiologic studies) can accurately
predict for clinical benefit from endocrine therapy. Accordingly, better methods for
predicting clinical response to antiestrogen therapy need to be developed.