Patients with metastasized melanoma, that progress upon standard of care therapy, have a bad prognosis and need new treatment options. Clinical trials showed that these patients may benefit from infusions with T cells that are able to recognize and kill their tumors. One approach to obtain such T cells is to isolate and expand tumor infiltrating lymphocytes (TIL), that are present in the patient’s own surgically resected or biopsied tumor tissue. We know that there is a huge variation in the number of immune cells that are present in different metastatic lesions within individual patients. Here we want to investigate whether TIL obtained from different lesions possess different characteristics that may affect their clinical efficacy. To this end the infiltration of various lesions will be visualized by a specific PET/CT technique allowing us to select two differentially infiltrated lesions as a source of TIL. Furthermore, we will evaluate if the infiltration level of the other lesions determines their response to subsequent TIL infusions. The results will give us clues how to further optimize TIL therapy.