AFP and choriocarcinoma: NGGCT with a yolk sac carcinoma or choriocarcinoma component secretes alpha-fetoprotein (AFP) or human chorionic gonadotropin (HCG) which can be detected in serum or cerebrospinal fluid.5 Previous studies have found that GCTs present with a characteristic “cardioid shape sign,” ie, the tumor invades the bilateral thalamus anteriorly.