ERBB2 and breast cancer: At our Institute, starting from the year 2019, HR+HER2‐advanced breast cancer patients treated with CDK4/6 inhibitors combined with aromatase inhitors or fulvestrant have been invited to participate in a study (Indaco Trial) aimed at the evaluation of biomarkers of efficacy and toxicity, which received formal approval by the Institutional Review Board (IRB) on the January 29, 2019, protocol number: RS1162/18(2179) RC18.