A yolk sac tumor is a rare, malignant germ cell tumor that typically arises in the gonads (testes or ovaries) but can also occur in other parts of the body. It is characterized by the presence of yolk sac elements and is often associated with elevated levels of alpha-fetoprotein (AFP). Yolk sac tumors are most found in children and young adults and can be treated with a combination of surgery, chemotherapy, and radiation therapy.