Abstract P2-26-12: Interaction between CTCs and platelets complicate their detection by masking surface epitopes

Abstract

Abstract 1) Background: It is well known that solid tumors have the ability to form metastases. The development of distant metastases is due to the primary tumor shedding cells that travel to distant sites via the blood vessels. Platelets specifically promote tumor cells survival in the bloodstream. To investigate the interplay between platelets and circulating tumor cells, we implemented our approach to label simultaneously circulating epithelial tumor cells and platelets. 2) Methods: 40 breast cancer patients were enrolled into the study. Blood samples were collected in EDTA tubes without fixatives and processed at 3 timepoints (0h, 24h and 48h) using the maintrac® approach. In order to visualize platelets we used anti-CD36 antibody staining. 3) Results: We observed at 0h post-blood draw platelet aggregates strictly attached to single cells that did not stain with anti-EpCAM antibody. After keeping blood samples at room temperature for 24h platelet aggregates could still be detected, but the anti-EpCAM antibody became accessible to the underlying cells. CTCs were detected in 94% of patients on day 1 post-blood draw. At 48h following initial blood drawing, platelets had almost completely disappeared from the cell surface and the number of detected CTCs remains stable between 24h and 48h. Furthermore, the number of CTCs correlates with clinical stage of disease. Patients with stage I/II have significantly less CTCs as compared to patients with stage III/IV (median 5 vs. 19 CTCs/100µl cell suspension, p< 0.05). 4) Conclusion: Our results suggest that platelets play a key role in masking circulating tumor cells. Masking may explain the difficulties in detection of these cells and prevention of their elimination by the immune system. Citation Format: Dorothea Schott, Monika PIZON, Katharina Pachmann. Interaction between CTCs and platelets complicate their detection by masking surface epitopes [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-26-12.