Genomic and expression profiling reveal molecular heterogeneity of disseminated tumor cells in bone marrow of early breast cancer

Detection of disseminated tumor cells (DTCs) in bone marrow is an established negative prognostic factor. We isolated small pools of (~20) EPCAM-positive DTCs from early breast cancer patients for genomic profiling. Genome-wide copy number profiles of DTC pools (n = 45) appeared less aberrant than the corresponding primary tumors (PT, n = 16). PIK3CA mutations were detected in 26% of DTC pools (n = 53), none of them were shared with matched PTs. Expression profiling of DTC pools (n = 30) confirmed the upregulation of EPCAM expression and certain oncogenes (e.g., MYC and CCNE1), as well as the absence of hematopoietic features. Two expression subtypes were observed: (1) luminal with dual epithelial–mesenchymal properties (high ESR1 and VIM/CAV1 expression), and (2) basal-like with proliferative/stem cell-like phenotype (low ESR1 and high MKI67/ALDH1A1 expression). We observed high discordance between ESR1 (40%) and ERRB2 (43%) expression in DTC pools vs. the clinical ER and HER2 status of the corresponding primary tumors, suggesting plasticity of biomarker status during dissemination to the bone marrow. Comparison of expression profiles of DTC pools with available data from circulating tumor cells (CTCs) of metastatic breast cancer patients revealed gene expression signatures in DTCs that were unique from those of CTCs. For example, ALDH1A1, CAV1, and VIM were upregulated in DTC pools relative to CTCs. Taken together, analysis of pooled DTCs revealed molecular heterogeneity, possible genetic divergence from corresponding primary tumor, and two distinct subpopulations. Validation in larger cohorts is needed to confirm the presence of these molecular subtypes and to evaluate their biological and clinical significance.
Genetics: two subtypes of disseminated tumor cells in bone marrow Tumor cells found in the bone marrow of women with early-stage breast cancer constitute molecularly distinct populations that could impact patient outcomes and treatment responses. Mark Jesus Magbanua and coworkers from the University of California, San Francisco, USA, performed genome-wide copy number variation analysis, expression profiling on 64 cancer-related genes and screened for PIK3CA mutations in pools of tumor cells isolated from bone marrow aspirates of patients undergoing surgery. These disseminated tumor cells (DTCs) contained fewer genomic abnormalities on average than their corresponding primary tumors, although the DTCs often acquired oncogenic mutations in PIK3CA. Expression profiling revealed two distinct subtypes of DTCs, both of which were different from circulating tumor cells found in the bloodstream. Further studies are needed to evaluate the biological and clinical significance of this molecular and genomic heterogeneity in DTCs.