The Testicular Cancer Resource Center

Extragonadal Germ Cell Cancer (EGC)

95% of all testicular tumors are germ cell tumors. That is, the tumors originate in the sperm forming cells in the testicles (the males gonads) or egg producing cells in the ovary (female gonads). Occasionally, however, germ cell tumors develop elsewhere in the body without any evidence of cancer in the testes. When this happens they are referred to as Extragonadal Germ Cell Tumors (meaning outside of the gonads).

During embryonic development (when you are but a clump of cells), germ cells are first seen outside of the embryo in the yolk sac. At about 4 to 6 weeks of development, these cells migrate into the embryo where they populate the developing testes or ovaries. If these cells miss their destination, they are likely to come to rest in one of a number of midline sites in the body. Extragonadal tumors arise when these cells become cancerous. In some cases, however, an apparent extragonadal tumor turns out to be a metastatic testicular tumor where the primary tumor has "burnt out" or died on its own.

Extragonadal germ cell tumors can take on a variety of tumor types. They can be either benign (teratoma) or malignant. Malignant tumors can be either seminoma [aka germinoma in females] or nonseminoma (embryonal carcinoma, immature teratoma, endodermal sinus tumor [aka yolk sac tumor], choriocarcinoma, and mixed germ cell tumors). Although much more common in males, extragonadal tumors can also occur in females.

The great majority (80%) of these tumors are benign and are handled with surgery alone. Most of the benign tumors occur in children. While benign tumors occur with equal frequency in men and women, malignant extragonadal tumors are much more common in males (9:1). Understand this, though: extragonadal germ cell tumors are rare, accounting for only 1 to 4% of all germ cell tumors.

This type of cancer is aggressive and is usually seen in young adults. Patients with mediastinal nonseminomatous EGC are typically classed as poor risk patients because these cancers often have unusual biological features that diminish cure rates and add additional complexities to treatment. Despite these unusual characteristics, about half of even these patients are cured. Other extragonadal sites do not share these same adverse biological features and are usually classified with an intermediate prognosis. For all extragonadal seminomas, the outlook is identical to metastatic testicular seminomas with the same high prospect of cure.

Extragonadal tumors can arise virtually anywhere in the body, but the site of origin is typically one of three locations:

The treatment and prognosis of the disease depends on a variety of factors including: the type of cancer, the tumor location, and the size of the tumor. Typically, seminomas (and germinomas) have a more favorable outcome than the other types of germ cell cancer.

Hidden or "burnt out" testicular lesions are important because detection can provide a superior treatment plan, and treatment of the hidden testicular lesion is also important. If you have extragonadal retroperitoneal tumors, do not be surprised if the doctors expend extra effort examining your testicles for a primary tumor.

Patients with EGC are very likely to benefit from the experience and expertise of a specialist in the field. We strongly recommend that you or your doctor contact an expert for treatment advice.

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This page was last updated on Mar 29, 2018
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