Dual-positive CTCs in patients with advanced breast cancer show metastatic potential and prognostic value

Metastasis is the leading cause of death in patients with breast cancer (BC), but the mechanisms underlying metastasis formation are still poorly understood. Circulating tumor cells (CTCs) are considered the main seed of metastasis with demonstrated prognostic impact in patients with BC. They are conventionally identified as cells positive for epithelial markers and lacking leukocyte markers. Nonetheless, circulating cells expressing both markers [dual-positive cells (DPcells)] have been reported but poorly investigated. Here, we evaluated, in a cohort of 340 patients with advanced BC, the prognostic impact of DPcells, showing their association with worse survival, particularly in patients with less than five CTCs. Their prognostic value varied among BC subtypes, with greater relevance observed in triple-negative and HER2-positive BC. Moreover, by performing single-cell genomic profiling of DPcells isolated from patients, we detected genomic aberrations in 28 and 93% of analyzed DPcells and CTCs, respectively. In vivo, DPcells were detected only in the blood of immunocompetent but not immunodeficient mice and no differences in the lung metastatic colonization ability of DPcells versus control cancer cells were observed. Our findings highlight the importance of studying this overlooked subpopulation of CTCs as a prognostic biomarker in BC, which might be particularly important in specific BC subtypes. Moreover, our results support the malignancy and metastasis-forming capability of DPcells and underline the need for future studies better defining the origin of these cells.