Tumor infiltrating lymphocytes (TILs) consist of lymphocytic cell lines that invade tumor tissue. The migration of TILs into malignant tissue has led to the suggestion of their use in the treatment of various cancers, including head and neck squamous cell carcinoma, melanoma, lung cancer, breast cancer, genitourinary cancers and a growing list of other malignancies. Additionally, TILs are emerging as an important biomarker in predicting the efficacy and outcome of treatment.