ERBB2 and breast carcinoma: Our findings on the drug acquisition costs are broadly consistent with three studies conducted in the USA and the UK that found that the major component of the pharmaceutical therapy costs is the CDKi treatment.31–33 The main driver of ADR costs was found to be the haematological adverse events, an outcome that is congruent with the findings of a study assessing the cost-effectiveness of palbociclib or ribociclib in the treatment of advanced HR-positive, HER2 breast cancer in the USA.33