Epithelial Mesenchymal Transition (EMT) refers to the transition of cells from a more differentiated epithelial phenotype to a less differentiated mesenchymal phenotype, a process that may be triggered by a range of therapeutic interventions including cytotoxic treatment, and which we have previously linked to poor breast cancer (BrCa) outcome after neoadjuvant chemotherapy (NAC)1. Mammographic breast density (MBD)represents the white radiographic appearance of epithelial and stromal breast tissue on a mammogram. High MBD in patients being treated for BrCa also associates with chemoresistance, correlating with lower pathological complete response rates (pCR)2. Linking these two stimuli, EMT can also be induced by artificial high-density stroma, where it also leads to chemoresistance in vitro3.

Here we set out to validate the link between poor outcome after NAC and EMT in a larger validatory patient cohort, and to ascertain the molecular drivers through which EMT is triggered in this setting. Further we look to confirm the association of high MBD with poor chemoresponse in the same cohort, and to assess whether this chemoresistance is mediated through EMT with the same drivers.

In a pilot cohort of 50 NAC-treated locally advanced BrCas with a pCR rate of 20%, pre-NAC biopsies and post-NAC surgical specimens were analysed for expression changes in a panel of EMT-related markers across treatment using 230 Nanostring assays. This included the EMT-driving transcription factors TWIST 1 and 2, SNAIL 1, 2 and 3 and ZEB 1 and 2, which were correlated with risk of relapse. Snail-3 showed significantly greater induction in relapsers compared to non-relapsers (OR=1.8, p=0.04) with a borderline significantly greater induction of TWIST-1 (OR=2.4, p=0.08) in relapsers in addition.

In a subsequent 240-patient validation cohort with a pCR rate of 18%, contralateral cranio-caudal view mammograms from the time of diagnosis have been collated and digitized with MBD assessment employing Cumulus software ongoing. Percent breast density will be assessed both as a continuous variable and by quartiles. Immunohistochemistry on pre- and post-operative tissue sections with pan-cytokeratin-vimentin co-staining to identify EMT and staining for SNAIL-3 and TWIST-1 is also in progress.

Associations between MBD, EMT before and after chemotherapy, pCR and relapse-free survival will be presented. The role of Snail-3 and TWIST-1 in the interplay between MBD, EMT and outcome is being explored and will be reported.

Citation Format: Agarwal V, Spalding LJ, Blick T, Dobrovic A, Thompson EW, Redfern A. The interplay between stromal density, epithelial mesenchymal transition and chemoresistance in breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-08-05.