This study explores the potential mechanism for cancer patients appearing vulnerable to SARS-CoV-2 and poor outcomes via integrative bioinformatics analyses for SARS-CoV-2-required genes (ACE2, TMPRSS2, ATP6AP1, ATP6V1A, CCDC22, NPC1, PIK3C3, and RAB7A), host genes, and variants related to SARS-CoV-2 susceptibility and COVID-19 severity. The gene discussed is PIK3C3; the disease is cancer.