Trophoblast Invasion Biology: From Normal Implantation to Accreta Spectrum and Choriocarcinoma

Trophoblast invasion is a finely regulated physiological process that demonstrates controlled cellular migration and vascular remodeling during human pregnancy. During normal implantation, cytotrophoblasts differentiate into extravillous trophoblasts (EVTs), which enter the maternal decidua and remodel spiral arteries, converting them into low-resistance vessels required for fetal nutrition. This balance of invasion and restraint promotes appropriate vascular adaptation at the maternal-fetal interface. Aberrations in this mechanism result in a range of pathological states, from excessive but non-malignant invasion in placenta accreta spectrum (PAS) to uncontrolled, malignant invasion in choriocarcinoma. In PAS, trophoblasts can infiltrate the myometrium due to dysregulated production of matrix metalloproteinases (MMP-2, MMP-9), integrins, and angiogenic factors (VEGF, HIF-1α). In choriocarcinoma, trophoblastic cells activate PI3K/AKT, Wnt/β-catenin, and Notch signalling, leading to hyperproliferation, immune evasion through PD-L1, and metastatic potential. Despite differences in clinical behaviour, many disorders have molecular mediators that link trophoblast invasion to vascular remodelling, angiogenesis, and immunological regulation. Emerging models including trophoblast organoids, placental explants, and placenta-on-a-chip technologies offer enhanced platforms to study such pathways at the cellular and molecular levels. This review highlights trophoblast invasion as a model of controlled angiogenic remodeling, providing mechanistic insight into both obstetric pathology and cancer biology. It underscores how studying placental invasion can inform therapeutic strategies targeting abnormal vascular invasion across diseases.