Yolk sac tumors (YST) are also known as endodermal sinus tumors (EST) and infantile embryonal carcinoma.

They are a type of germ cell tumor that can be found in infants and adults. Germ cells are cells that develop in the embryo and eventually grow to become the cells that make up reproductive organs. While very rare, yolk sac tumors in infants are the most common testicular tumor found in male children under age three.

Although yolk sac tumors are usually benign, the type known as endodermal sinus tumors are malignant. Yolk sac tumors can occur in both males and females, with the tumor in females occurring in the ovaries. The cause of these tumors is not known.

Signs & Symptoms

There are very few signs and symptoms of yolk sac tumors. In children the tumor often presents itself as a mass in the testicle that is painless. In adults a yolk sac tumor is most often part of a larger tumor. In both cases a biopsy of the cells will need to be done to provide a definitive diagnosis. Elevated serum alpha-fetoprotein (AFP) levels are one indication of yolk sac tumors.

Diagnosis

Testing is done to look for elevated levels of alpha-fetoprotein (AFP) or GAGA-4 as indicators that the tumor is in fact a yolk sac tumor. A biopsy of the cells gives a more accurate diagnosis.

Treatment

Treatment of yolk sac tumors depends on the size and stage of the tumor. In adults it will also depend on what is happening with the other tumors that the yolk sac tumor is a part of. Treatment usually involves a combination of surgery and chemotherapy.

Prognosis

Left untreated yolk sac tumors can be deadly. However, with proper treatment the prognosis is very good. Young children especially have a high recovery rate. The advances in chemotherapy in recent years have greatly improved the prognosis for these tumors.