Management must be individualized, integrating oncologic urgency, fetal safety, and limited validated evidence in this unique setting.<h4>Case summary</h4>We present the case of a 36-year-old woman diagnosed during the second trimester of pregnancy with HER2-positive (HER2+), node-positive (cT2[m]N3a) breast cancer (BC). This evidence concerns the gene ERBB2 and breast cancer.