Regarding testis cancer, AFP has been demonstrated to be secreted by NSTs (primarily by yolk sac tumor and, to a lesser extent, by embryonal carcinomas) and not by SEs; therefore, patients with an elevated protein level should present a non-seminomatous component of testis cancer, opening the way to the improvement in the specificity of AFP detection in the sera of patients with NSTs. Here, AFP is linked to yolk sac tumor.