The intersection of anchoring placental villi and maternal decidua morphologically resembles the invasive margin of carcinomas and contains trophoblast cells that express high levels of immunomodulatory proteins and growth factors implicated in tumour severity, including PD-L1, IDO-1, TIM3, HER2 and EGFR27,55,56. The gene discussed is ERBB2; the disease is carcinoma.