KRT18 and yolk sac tumor: Therefore, serum Ck-18 is more valuable than serum AFP for the diagnosis of HCC in contrast to Dom-Gene et al., [27] who said that Ck-18 is less valuable than AFP for the diagnosis of HCC because AFP is produced by the tumor, and only tumors originating in the gastrointestinal tract or yolk sac tumors complicated by hepatic metastases are likely to be mistaken clinically for HCC.