Primary Mediastinal Seminoma

Abstract

The histologic appearance of primary mediastinal and testicular seminomas is identical; therefore it is always important to rule out metastatic testicular disease in patients with suspected primary mediastinal seminoma. The histogenic origin of extragonadal germ cell tumors has been a matter of controversy. In 1946 Schlumberger proposed that these tumors were of thymic origin and were the result of disordered somatic cell development [1], This theory failed to explain the presence of germinomatous elements in mixed tumors which could not have arisen from somatic tissue [2]. Others have argued that mediastinal seminoma represents metastatic disease, and that the primary testicular tumor is either occult or has undergone spontaneous regression. Clinical and postmortem studies do not support the theory of metastatic mediastinal disease from an occult testicular primary. In addition the theory does not explain the finding of mediastinal seminoma in women. In 1951, Friedman proposed a theory supporting the existence of primary extragonadal germ cell tumors which has become generally accepted [3]. The theory states that displaced primordial germ cells, which are located along the midline, are the origin for all extragonadal germ cell tumors. In this theory, the different morphologic patterns of germ cell tumors resulted from different stages of tumor differentiation.