HBG2 and neuroendocrine carcinoma: The aim of this study is to develop a population pharmacokinetic-pharmacodynamic (PK/PD) model for triapine to describe the PK parameters, the effect of smoking on exposure, and the relationship between methemoglobin concentrations and exposure.<h4>Methods</h4>A total of 36 patients with advanced stage cervical or neuroendocrine cancers from two phase I studies were included in the population PK/PD model building.