Photoimmunotherapy is a new cancer treatment that uses cetuximab sarotalocan sodium, a conjugate of cetuximab and the light activatable dye, IR700, and red light at a wavelength of 690 nm. In Japan, photoimmunotherapy for "unresectable locally advanced or locally recurrent head and neck cancer" has been covered by insurance since 2021. Although presently approved only for head and neck cancer, photoimmunotherapy is an important technology in the future of various cancer treatments. Photoimmunotherapy is an important technology for the future of various cancer treatments, and it is essential to strive for the development and widespread use of photoimmunotherapy in clinical practice. In this review, we will explain the mechanism of photoimmunotherapy, treatment cases, clinical trial data, reports from real world data in Japan, and future issues and prospects as seen in actual clinical practice.