Mechanisms of pregnancy-associated triple negative breast cancer risk: insights from spatial omics

Pregnancy-associated triple-negative breast cancer (PA-TNBC) is a highly aggressive, hard-to-treat malignancy, with increased risk linked to post-lactational mammary gland involution. To understand this, we used GeoMx Digital Spatial Profiler to analyze the transcriptional landscape of 46 treatment-naïve PA-TNBC tissues from 33 women (10 pre-involution/PRE; 23 post-involution/POST, diagnosed within 3 years of delivery), focusing on epithelial and microenvironmental changes. Our findings reveal that the most significant transcriptional differences between PRE and POST exist in non-invasive epithelia and during the transition to invasion. POST non-invasive epithelia showed distinct activation of inflammatory and developmental pathways, while transitioning to TNBC involved elevated chromatin remodeling and migration. Notably, the tumor microenvironment (TME) surrounding POST invasive epithelia featured the greatest immune cell infiltration yet also increased immune exhaustion. Pseudotime analysis highlighted the 1-2 year postpartum window as having the strongest inflammatory signaling. These results underline the need for early molecular detection in normal-appearing post-involution tissues and suggest that targeting the TME is a viable strategy for treating POST PA-TNBC.