Studies have shown that photodynamic therapy (PDT) causes or enhances an antitumor immune response. Moving from a mouse model in lung cancer to a translational approach, researchers are conducting an ongoing observational study to determine whether the immune response in patients with lung cancer treated with PDT is mediated by a T-cell phenotype, which may result in decreased tumor size and potentially improve survival. Preliminary findings focus on certain inflammatory cytokines that may be predictive of these T-cell phenotypes, such as interleukin (IL)-12, IL-4, T-regulatory cells, and T helper 17 cells. Correlation of the immunobiology of PDT associated with outcomes and surrogate markers may allow clinicians to predict improvement in patients treated with PDT and improve prognostic counseling.