Cancer immunotherapy has emerged as one of the most powerful anticancer therapies. However, the details on the interaction between tumors and the immune system are complicated and still poorly understood. Optical fluorescence imaging is a technique that allows for the visualization of fluorescence-labeled immune cells and monitoring of the immune response during immunotherapy. To this end, near-infrared (NIR) light has been adapted for optical fluorescence imaging because it is relatively safe and simple without hazardous ionizing radiation and has relatively deeper tissue penetration into living organisms than visible fluorescence light. In this review, we discuss state-of-the-art NIR optical imaging techniques in cancer immunotherapy to observe the dynamics, efficacy, and responses of the immune components in living organisms. The use of bioimaging labeling techniques will give us an understanding of how the immune system is primed and ultimately developed.

Among modalities of cancer immunotherapy, near‐infrared photoimmunotherapy (NIR‐PIT) has reached significant preclinical and clinical stages and quickly evolved over the last 5 years. NIR‐PIT uses deep‐penetrable NIR light to induce physicochemical changes in the antibody–photosensitizer conjugate (APC), leading to resultant necrosis and immunogenic cell death (ICD) of the cancer cells. Alternatively, other types of photomedicine use photosensitizers to convert absorbed light energy either into reactive oxygen species for photodynamic therapy (PDT) or into heat for photothermal therapy (PTT). ICD is a unique and relevant outcome of NIR‐PIT because it induces long‐lasting antitumor host immunity, which overcomes the immunosuppressive network of cancer. Due to its high specificity and durable antitumor effects, NIR‐PIT is now considered a promising cancer therapy, and optimized NIR‐PIT is readily expanding its applicability to many different types of cancer. Along with the traditional method of NIR‐PIT, new avenues in its realm of treatment are currently being explored, such as the targeting of other immunosuppressive elements, delivery of NIR light through a catheter, real‐time imaging for tumor detection, and the use of tumor‐seeking small molecules for improved efficacy and safety. In addition, its effect on hyperpermeability has opened a door for a wide array of combination therapies with other modalities. This review summarizes the recent findings in clinical and preclinical studies of NIR‐induced photomedicine and its future significance in the field of cancer research.