Abstract P4-01-07: Clinical relevance of CK+/CD45+, dual-positive circulating cells (DPCells) in patients with metastatic breast cancer (MBC)

Abstract

Abstract Background: The prognostic impact of circulating tumor cells (CTCs) in patients with breast cancer is well recognized. Nonetheless, by using the FDA-approved CellSearch™ platform, CTCs are detected only in a fraction of patients, both in early and metastatic breast cancer. Several investigators reported the presence of circulating cells expressing both epithelial and leukocyte markers (dual-positive cells, DPcells) in the blood of patients with breast cancer. In view of the fact that those cells do not meet the conventional CTC-identification criteria, they were never investigated or considered not relevant. Recently, we demonstrated that circulating DPcells collected from cancer patients’ blood can have an aberrant genome (1), indicating them as bona fide DP circulating tumor cells (DP-CTCs). Here, we investigated the clinical relevance of circulating DPcells in patients with metastatic breast cancer (MBC). Methods: Blood samples (7.5 ml) were collected from patients with MBC before starting new therapy. All patients were enrolled in a prospective clinical trial. Samples were processed with the FDA-approved CellSearch™ platform (Menarini Silicon Biosystems, Italy) for CTC and DPcell counting. DPcells identification criteria were positive nuclear staining plus expression of both CK and CD45. The conventional threshold of ≥5 CTC/sample was used for CTCs prognostic stratification, while the positivity cutoff for DPcells was ≥1 DPcell/sample. Results: Blood samples (n= 136) were collected from 136 patients with luminal (n= 72), triple negative (TN, n= 30) and HER2+ (n= 34) MBC. In 51 samples (38%) ≥5 CTCs were observed (CTCpos), while 85 patients (62%) presented <5 CTCs (CTCneg). DPcells were found in 68 patients (50%) which were either CTCpos or CTCneg (31 and 37 patients, respectively). DPcell presence was not associated with CTCs. DPcells were more frequent than CTCs in patients with HER2+ (59% vs. 24%) and TN (53% vs. 30%) BC, but not in the samples from patients with luminal disease (46% vs. 47%). Moreover, in the majority of HER2+ and TNBC DPcellpos patients, DPcells were not detected in association with CTCs (70% and 56%, respectively). While in most DPcellpos patients with luminal MBC, DPcells were present together with CTCs (58%). Overall survival (OS) and progression free survival (PFS) related to DPcell- and CTC-positivity were assessed in 125 and 82 patients respectively. No statistically significant association between DPcells and OS was observed. DPcells were instead associated with PFS: Median PFS= 4.27 vs. 6.70 for DPcellpos and DPcellneg patients, respectively (p= 0.046). Interestingly, by combining CTC- with DPcell-stratification, we observed that among CTCneg patients (n=51), those with DPcells (n=21) experienced a shorter PFS with respect to DPcellneg ones (median PFS= 5.67 vs. 9.33 months, p= 0.041). While no difference was observed between median PFS of CTCpos/DPcellpos and CTCpos/DPcellneg patients: 3.57 and 3.63 months, respectively. Conclusions: This is the first study investigating the clinical relevance of DPcells. The data indicate that DPcells are detectable in patients with MBC, in particular in those subtypes where CTCs are less frequent (HER2+ and TNBC). Moreover, the presence of DPcells is associated with shorter PFS. These data suggest that DPcells could constitute a new prognostic biomarker in treatment-refractory non-luminal MBC, especially in CTCneg patients. Further studies are needed to validate these preliminary results and to better define the clinical utility of this new CTC subpopulation. Refernces: 1. Reduzzi C, et al. The curious phenomenon of dual-positive circulating cells: Longtime overlooked tumor cells. Submitted to Seminars in Cancer Biology Citation Format: Carolina Reduzzi, Lorenzo Gerratana, Youbin Zhang, Vera Cappelletti, Maria Grazia Daidone, Massimo Cristofanilli. Clinical relevance of CK+/CD45+, dual-positive circulating cells (DPCells) in patients with metastatic breast cancer (MBC) [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-01-07.