MSLN and yolk sac tumor: Ordóñez demonstrated that non-mucinous carcinomas of the ovary most frequently exhibited strong MSLN reactivity; however, they observed that this marker was also expressed in other non-mucinous carcinomas, such as clear-cell carcinomas of the ovary, endodermal sinus tumours, as well as clear-cell and transitional-cell carcinomas of the ovary [21].