AFP and yolk sac tumor: Looking closer at the preoperative STM levels, specimens containing yolk sac tumor had significantly higher AFP levels (mean AFP level = 1801 μg/l) than specimens containing embryonal carcinoma (mean AFP level 303 μg/l, one-tailed t test, p = 0.0412) or teratoma (mean AFP level 224 μg/l, one-tailed t test, p = 0.035).