A yolk sac tumor is a type of germ cell tumor that primarily affects children and young adults. It originates from the cells that would normally develop into the yolk sac during early embryonic development. These tumors can occur in the ovaries, testes, or other areas of the body and are known for their rapid growth. Yolk sac tumors are often diagnosed through imaging tests and blood tests that measure specific tumor markers, such as alpha-fetoprotein (AFP). Treatment typically involves a combination of surgery, chemotherapy, and sometimes radiation therapy, depending on the tumor's stage and location.