Although this example is rather contrived—as trastuzumab is typically funded for patients in high-income countries for this age group—it does demonstrate that if heterogeneity in baseline prognosis was incorporated into the economic evaluation, a policy-maker may consider funding trastuzumab for the subgroup of HER2+ breast cancer patients with the poorer prognosis (ER−) subtypes (as it is more cost-effective). Here, ERBB2 is linked to breast cancer.