A phase II trial that addressed the effect of combining seribantumab with exemestane in metastatic heregulin (HR) positive (ER+ or PR+) breast cancer was stopped due to the significant side effects [81], while a phase II clinical trial examining the effect of combining seribantumab with fulvestrant in NRG-positive, Her2− breast cancer patients is still ongoing [82]. The gene discussed is ESR1; the disease is breast cancer.