While associations between prevalence and outcome for some immune populations, such as B cells, remain unclear, the positive prognostic value of cytotoxic (CD8) tumor infiltrating lymphocytes (TIL) has been demonstrated in multiple solid tumor types including breast [5,6] and colorectal cancer [7,8,9] as well as melanoma [10,11,12,13], bladder [14,15], prostate [16,17], ovarian [18,19], pancreatic [20,21], and, when associated with proliferative index, renal cell carcinoma [22]. The gene discussed is CD8A; the disease is melanoma.