Strictly applying a “rule of thumb” cost-effectiveness threshold of gross domestic product per capita (NZ$45,000 [2011 PPP-adjusted: US$30,300; €23,700; £21,200]), our NZ study suggests that trastuzumab may not be cost-effective for patients with ER+ node-positive HER2+ breast cancer (approximately 61% of expected node-positive HER2+ early breast cancer patients) [3], and that trastuzumab is highly cost-effective up to the age group 40–44 y for ER−/PR+ breast cancer (3% of cases) [3] and up to the age group 65–69 y for ER−/PR− breast cancer (37% of cases) [3]. The gene discussed is ESR1; the disease is breast cancer.