To determine whether inhibition of JNK signaling sensitizes mammary tumors and lung metastases to chemotherapy, we treated tumor‐bearing NSG mice with JNKi starting at 5 days post‐implantation of MDA231‐LM2 or SUM159‐LM1 cells and initiated paclitaxel treatment at day 10 post‐implantation (Fig 7A). This evidence concerns the gene MAPK8 and breast cancer.