Investigation of EpCAM negative CTCs as a prognostic and predictive biomarker in metastatic breast cancer

Aim Circulating tumor cells (CTCs) are considered as precursors of distant metastatic spread and can act as a prognostic and predictive biomarker. Their enrichment is mainly based on immunomagnetic technologies targeting antibodies against the epithelial cell adhesion molecule (EpCAM). However, it was shown that CTCs with low expression of EpCAM are not captured by such approaches.

Therefore, we compared EpCAM dependently and EpCAM independently isolated CTCs regarding their utility as a prognostic and predictive biomarker.

Material & methods CTCs were enriched from blood samples or EpCAM depleted blood fractions (EDF) of metastatic breast cancer patients using antibodies targeting EpCAM or Trop-2 and CD-49f in the CellSearch system. Their phylogenetic relationship was examined by low pass sequencing comparing predictive mutations.

Results Cell enrichment with antibodies targeting Trop-2 and CD-49f increased the CTC-positivity rate from 77.8% to 88.9% compared to EpCAM-based enrichment alone. Analysis of the EDF confirmed that a certain CTC population can be captured using the Trop2/CD49f antibody cocktail, that was missed out by targeting EpCAM. Combining both approaches, CTCs were detected in 100% of the analyzed blood samples. CTC numbers measured with both methods correlated with progression free and overall survival. Despite morphological differences – Trop2/CD49f-based enriched CTCs were smaller and less circular – CTCs enriched with both strategies presented similar genomic aberrations and identical predictive mutations.

Conclusion CTCs enriched EpCAM-based or Trop2/CD49f-based represent similar genomic tumor cell clones. Therefore, EpCAM negative CTCs could be used as a tumor surrogate material of clinical relevance, especially if no EpCAM-positive CTCs are detected.

Publication History

Article published online:
11 October 2022