PDCD1 and neoplasm: The repeated occurrence of spontaneous deaths could indicate other complications such as tumor spread, (uro)sepsis, anti-PD1 side effects, etc. Although there are no reports of direct immunotoxicity of anti-PD1 therapy in the Hgf-Cdk4R24C mouse strain in previous studies [62], it is possible that anti-PD1 therapy affects the local tumor-microenvironment which may impact tumor growth and invasiveness.