During his research career, Michael Mackey, Joseph Morley Drake Professor Emeritus of Physiology in the Department of Physiology at McGill University, Canada, made numerous consequential insights into biological mechanisms of dynamic hematologic diseases and gene regulatory networks. Throughout, he emphasized the importance of data on mathematical model conceptualization, development, calibration, and validation. This brief review describes contributions by Michael Mackey and his collaborators toward understanding and treating chemotherapy-induced neutropenia, a frequent and serious toxic side effect of cytotoxic chemotherapy, using data-driven mathematical models.