MMP‐9 is an enzyme secreted by pulmonary and immune cells that is active during embryonic development for lung branching morphogenesis and angiogenesis, processes that may be aberrantly activated during lung cancer, and is associated with all stages and poor prognosis for lung cancer (Atkinson & Senior, 2003; Cabral‐Pacheco et al., 2020; Wei, 2023). The gene discussed is MMP9; the disease is lung cancer.