One colorectal cancer patient with long-term anti-PD-1 monotherapy developed cytokine release syndrome (CRS) 5 days after receiving the Pfizer-BioNTech mRNA COVID-19 vaccine with evidence of increased inflammatory markers and elevated cytokine levels (IFN-γ, IL-2R, IL-18, IL-16, and IL-10) (32). This evidence concerns the gene IL18 and colorectal cancer.