This drug class is associated with an increased risk of angioedema in patients on ACEI [Odds ratio: 4.6 (95% confidence interval 1.6–13.3)] owing to inhibition of a kininase (dipeptidylpeptidase 4 (DDPIV)).22 The fourth patient who was suffering from relapsing prostate cancer had recently started taking estrogen, a hormone known to trigger acute attacks in hereditary angioedema.23 To our knowledge, this is, however, the first reported case of an estrogen-triggered attack in a patient with ACEI-AAE. The gene discussed is DPP4; the disease is prostate cancer.