Manganese (Mn), an essential trace mineral in the human body, plays a pivotal role in activating the host immune system via the cyclic guanosine monophosphate–adenosine monophosphate (GMP–AMP) synthase (cGAS)–stimulator of interferon genes (STING) pathway, enhancing anti-tumor immunotherapy [18]. The gene discussed is CGAS; the disease is neoplasm.