Abstract TC-02: When to do a window trial

Abstract

Abstract The window of opportunity in the short time between diagnosis and surgery for primary breast cancer has been exploited in trials of many endocrine agents. In these cases the therapeutic effect is antiproliferative and immunohistochemical detection of changes in Ki67 are considered a valid biomarker of likely long term efficacy. Trials have also been extended to assessment of inhibitors of growth factor receptors (eg lapatinib) and COX2 inhibitors. In these circumstances the mode of action is not purely inhibition of proliferation such that while changes in Ki67 may be of interest they should not be taken as necessarily reflecting the presence or absence of efficacy. It is also important to recognise that it may take longer than the time window available to get to a pharmacodynamic steady state. This is reflected by data from studies of tamoxifen and of GnRH analogues in premenopausal women. As well as being a window for assessing the biologic effectiveness of new agents it has been used as a means of assessing the prognosis of patients taking an established drug such as an aromatase inhibitor (AI) in the POETIC and an AI or tamoxifen in the ADAPT trial. Citation Format: M. Dowsett, S. Hurvitz. When to do a window trial [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr TC-02.