Oncological orthodoxy holds that (metastatic) breast cancer is an incurable disease. Response evaluation in metastatic breast cancer is determined by clinical, biochemical and radiological parameters, FDG PET CT being the imaging modality of choice for most types of breast cancer. However, even in cases where FDG PET CT and/or normalisation of serum tumour markers imply complete response to systemic therapy, durable disease-free survival is uncommon. To explore the mechanistic basis underlying persistent disease in spite of apparently effective systemic therapy, we hypothesized that Circulating Metastatic Disease (CMD) in the form of viable tumor cells or clusters might be a feature of persisting breast cancer. To address this, we obtained 15ml of peripheral blood from 927 known and previously treated cases of breast cancers immediately prior to FDG PET CT restaging. Peripheral blood mononuclear cells (PBMCs) were harvested by centrifugation. Circulating Ensembles of Tumor Associated Cells (C-ETACs), which are clusters of heterotypic apoptosis resistant cells of tumorigenic origin were enriched by a novel process using a combination of commercially available stabilizing agents. C-ETACs were characterized by immunostaining for EpCAM, pan-CK and CD45 as well as GCDFP-15 or GATA3. 927 patients underwent FDG PET CT of whom 731 (78.9%) had evidence of FDG avid residual disease. 196 patients (21.1%) had no metabolically active disease, among whom C-ETACs were detected in 171/196 cases (87.2%). The presence of CMD in a high proportion of cases in patients with no evidence of metabolically active disease implies that the majority of patients in whom conventional parameters of disease are negative have residual disease and are not biologically cured.

Citation Format: Ajay Srinivasan, Dadasaheb Akolkar, Darshana Patil, Timothy Crook, Cynthe Sims, Revati Patil, Vineet Datta, Anantbhushan Ranade, Pradip Fulmali, Pradip Devhare, Pooja Fulmali, Shoeb Patel, Akshay Ainwale, Sneha Puranik, Rajan Datar. Viable circulating ensembles of tumor associated cells persist in patients with no radiologically detectable disease after treatment in breast cancer [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 P4-01-17.