Abstract 2397: Evaluation of proliferation and apoptosis markers in circulating tumor cells (CTCs) of women with early breast cancer who are candidates for tumor dormancy

Abstract

Abstract Background: In breast cancer (BC) recurrences frequently occur many years after removal of the primary tumor. These relapses are thought to originate from cells that disseminated from the primary tumor and underwent a period of inactivity, called tumor dormancy, followed by active growth. Clinical dormancy could be related to the presence of solitary dormant cells (cellular dormancy), and/or micrometastases, in which cell proliferation is counterbalanced by apoptosis (tumor mass dormancy). Clinical cancer dormancy is frequently observed in BC, whereas CTCs have been identified in clinically disease-free BC patients 7-22 years after surgery. In the present study, we aimed to detect and characterize CTCs of dormancy candidates with BC by analyzing the expression of proliferation and apoptosis markers. Patients and Methods: A total of 104 patients with early BC presenting no evidence of disease for at least 5 years after initial diagnosis were included. In addition, 36 patients relapsing at least 3 years after initial diagnosis were also included as controls. Cytospins were prepared from peripheral blood mononuclear cells (PBMCs), obtained from dormancy candidates and metastatic BC patients at the time of follow-up and prior to the initiation of and first-line therapy, respectively. Samples were stained with pancytokeratin antibody along with ki-67 as a proliferation marker and M-30 an antibody recognizing a neo-epitope expressed only after caspase cleavage of cytokeratin 18 during early apoptosis. A total of 106 PBMCs per patient were analyzed by the use of ARIOL system. Results: CTCs were detected in 40 (36%) out of 104 dormancy candidate patients with early BC. In 25 (63%) of these patients, all CTCs detected were negative for both ki-67 and M30, whereas in 8 (20%) ki-67 positive CTCs, and in 9 (23%) M-30 positive CTCs were detected. Two (5%) patients had CTCs expressing either ki-67 or M30. Among a total of 223 CTCs detected, 194 (87%), were both ki-67 and M-30 negative, 8 (3%) were ki-67 positive and 20 (9%) were M-30 positive. In the group of 36 patients with metastatic disease, CTCs were identified in 10 (28%). In 4 (40%) patients, ki-67 positive CTCs (p=0.01 compared to dormancy candidates) were detected, whereas, no M-30 positive CTCs were observed. Among of total 126 CTCs identified, 50 (40%) were ki-67 positive (p=0.01, compared to dormancy candidates). Conclusions: CTCs are often detected in dormancy candidates with BC. The great majority of these CTCs express neither proliferation, nor apoptotic markers, thus possibly representing dormant CTCs. On the contrary, in patients relapsing long after initial diagnosis, the proliferation index is increased in CTCs. The above findings suggest that proliferation marker expression in CTCs could be used for monitoring disease progression in dormancy candidates with BC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2397. doi:1538-7445.AM2012-2397