Abstract P2-02-16: The proliferation index of circulating tumor cells (CTCs) is not influenced by the administration of adjuvant chemotherapy in early breast cancer (BC) and seems to reflect Ki67 expression of the primary tumor

Abstract

Abstract Background: The assessment of Ki67 in the primary tumor represents a prognostic marker with potential predictive implications in early BC. We evaluated Ki67 expression in CTCs from patients with early BC and assessed the effect of adjuvant chemotherapy as well as Ki67 expression in the primary tumor. Methods: Ki67 was evaluated in CTCs of 97 patients with early BC pre- and post- adjuvant chemotherapy by the use of immunofluorescence analysis. Cytospins of peripheral blood mononuclear cells were double stained with A45-B/B3 cytokeratin mouse antibody and a Ki67 rabbit antibody. Ki67 staining of the primary tumor was also performed for 13 CTC-positive patients. A proliferation index (PI) in CTCs was considered as the ratio of Ki67-positive CTCs/total CTCs. A PI of up to 14% was defined as 'low' whereas a PI above 14% was defined as 'high'. Results: CTCs were detected in 26 (26.8%) patients before and/or after chemotherapy. Seven (27%) of 26 CTC-positive and 8 (11%) of 74 CTC-negative patients relapsed (p = 0.047). Ki67-positive CTCs were identified in 20 (76.9%) of 26 patients, whereas in 1 (3.9%) and 5 (19.2%) patients, exclusively Ki67-positive and Ki67-negative CTCs, respectively, were detected. Seven (33%) of 21 Ki67-positive patients relapsed in contrast to none among the exclusively Ki67-negative patients (p = 0.13). A total of 154 and 161 CTCs were detected pre- and post-chemotherapy, respectively; the PI in CTCs was 56% and 55%, respectively. In 8 patients with detectable CTCs at both time points, the PI was 65% and 49% pre- and post-chemotherapy, respectively. In 5 (62.5%) out of 8 patients, the PI remained high, in 2 (25%) increased and in 1 patient no Ki67–positive CTCs were detected post-chemotherapy. Seventeen patients were CTC-positive at baseline [HER2 positive, n=5; triple negative, n=1; hormone receptor positive, n=11]. A concordance in Ki67 staining between the primary tumor and CTCs was recorded in 10 (77%) out of 13 patients. Moreover, in 2 (67%) of 3 patients with exclusively Ki67-negative CTCs, low Ki67 expression was also observed in the primary tumor. Interestingly, 2 out of 5 patients with HER2 positive primary relapsed and both had high PI in their CTCs, whereas 2 out the 3 HER2 positive patients that did not relapse had low CTC proliferation index. Similarly, the triple negative patient had low PI in her CTCs and has not relapsed after 4 years of follow up. Conclusions: Adjuvant chemotherapy fails to decrease the proliferation index in CTCs. Ki67 expression in CTCs seems to reflect Ki67 expression in the primary tumor and could be predictive of patient outcome. Citation Format: Agelaki S, Spiliotaki M, Spanaki A, Kassiou L, Tzardi M, Koinis F, Kafousi M, Georgoulias V, Mavroudis D. The proliferation index of circulating tumor cells (CTCs) is not influenced by the administration of adjuvant chemotherapy in early breast cancer (BC) and seems to reflect Ki67 expression of the primary tumor. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-02-16.