CD4 and neoplasm: Although the PD-1 pathway is widely known for its role in T-cell exhaustion and tumor immunosuppression, PD-1 is not an exhaustion-specific marker as it is also expressed on all conventional CD4+ T cells and CD8+ T cells during acute T-cell activation.25 Given the acute setting of hyperthermic cisplatin exposure and short duration of a few hours between the collection of pre- and post-HIPEC tumors, we interpret the immediate PD-1 expression after HIPEC as a marker of T-cell activation.