Adjuvant Lapatinib and/or Trastuzumab Treatment Optimisation (ALTTO), a randomized, multi-center, open-label, phase III study of adjuvant lapatinib plus trastuzumab treatment in patients with HER2/ERBB2 positive primary breast cancers (ClinicalTrials.gov, identifier NCT00490139), as well as other clinical trials with double ERBB2 blockade, support the safety of lapatinib plus trastuzumab treatment, since a lower, although not statistically significant, incidence of cardiac events was detected in patients in the trastuzumab plus lapatinib arm. The gene discussed is ERBB2; the disease is breast cancer.