Upon analyses of HER2-positive breast cancer samples from treatment-naive patients and residual disease at surgery after neoadjuvant anti-HER2 therapy, including paired samples from the phase II SOLTI-1114 PAMELA trial, we observed that anti-HER2 treatment or resistance to anti-HER2 therapy both resulted in increased RANK expression. The gene discussed is ERBB2; the disease is breast carcinoma.