IDO1 and cancer: The three downstream consequences of the ‘cytokine storm’—viz suppressed pineal melatonin, increased gut permeability/dysbiosis and activation of the IDO/kynurenine/AhR pathway—have relevant pathophysiological consequences and are also important to how pre-existent, high-risk medical conditions prime for severity and fatality in SARS-CoV-2 and cancers.