An Accessible Recirculating Organ-on-a-Chip Model of Pregnancy-Associated Breast Cancer Reveals ER Stress-Driven Tumour-Placental Cross-Talk

Pregnancy-associated breast cancer (PABC) is more aggressive and has a poorer prognosis than non-pregnant breast cancer, yet no preclinical model recapitulates the tumour-placental cross-talk underlying the disease, a major barrier to developing therapies safe for both mother and fetus. We address this with an accessible PABC organ-on-a-chip model built from commercial components. Two single-channel chips seeded with breast cancer and trophoblast cells are coupled into one closed recirculating loop, where a shared medium carries each compartment's secreted factors to the other under physiological shear. This architecture sustains the systemic, bidirectional cross-talk central to PABC that static and single-compartment models cannot, yet needs no microfabrication and runs in any standard laboratory. Using cell-cycle-resolved transcriptomics and secretomics, we found that flow-driven cross-talk activates endoplasmic reticulum stress, marked by HSPA5 upregulation in both cell types, driving tumour invasion, placental dysfunction, and DNA-repair dysregulation. Key molecular signatures aligned with clinical PABC datasets, confirming model relevance. As proof-of-concept, antioxidant coenzyme Q10 reduced trophoblast HSPA5. The model offers a reproducible, accessible system for studying PABC and for screening novel interventions.