Abstract P2-10-05: PowerPIINC trial: Changes in tumor proliferation index and quality of life with 7 days of preoperative tamoxifen

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Abstract BACKGROUND: A decrease in Ki67 has been shown to be a predictor of response to tamoxifen. Previous trials have shown a decreased Ki67 proliferation index in breast tumors with as little as 2 weeks of preoperative tamoxifen. However, shortening the preoperative treatment time in window of opportunity studies increases patient acceptance for trial participation. The POWERPIINC trial examined the effect of 7 days of preoperative tamoxifen on breast tumor proliferation and patient symptoms. METHODS: Adult women with untreated stage I or II invasive breast cancer that was ER positive (>1%) planning on breast surgery with no contraindications to tamoxifen were enrolled. Women received 20mg of tamoxifen for 7 days up to the day of surgery and for 14 days afterwards. Proliferation was assessed by Ki67 immunohistochemistry before and after 7 days of tamoxifen. The proliferation genes from the PAM50 were also assessed by RT-PCR. Symptoms and QOL were assessed by the FACT-ES, MENQoL, and BMQ. RESULTS: 52 women were enrolled, and 44 were evaluable for Ki67. The median age was 58.5 years, and the median tumor diameter was 1.2cm. Most women (73%) were post-menopausal. Most tumors were PR positive (88%). Only 8% of tumors were HER2-positive. The Ki67 decreased by a geometric mean of 40% (95% CI 29%-63%), and 73% (95% CI 57%-85%) of women had tumors with decreased proliferation after 7 days of tamoxifen (p=0.0001 by paired t-test). No correlation was seen between the change in Ki-67 and change in FACT-ES or MENQoL scores. Women reported minimal to no bother from psychosocial or physical symptoms at baseline or on the day of surgery. Expression level of individual proliferation genes did not change after 7 days of tamoxifen. CONCLUSION: Seven days of tamoxifen showed a similar relative decrease in the Ki67 proliferation index as that reported for longer courses. Therefore, short window of opportunity trials can be informative. Citation Format: Cohen AL, Factor RE, Mooney K, Wade M, Serpico V, Salama M, Nelson E, Porretta J, Matsen C, Ostrander E, Bernard P, Boucher K, Neumayer L. PowerPIINC trial: Changes in tumor proliferation index and quality of life with 7 days of preoperative tamoxifen [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P2-10-05.