PRIMARY GERM-CELL TUMORS OF THE MEDIASTINUM .2. MEDIASTINAL SEMINOMAS- A CLINICOPATHOLOGICAL AND IMMUNOHISTOCHEMICAL STUDY OF 120 CASES

BACKGROUND. Primary seminomas of the mediastinum are unusual neoplasms that are morphologically indistinguishable from their gonadal counter parts but may have different biologic behavior because they arise at t his particular location.METHODS. The clinical and pathologic features in 120 cases of primary mediastinal seminoma were reviewed, and the im munohistochemical staining patterns in 50 of these tumors were also an alyzed. RESULTS. The patients were all men between the ages of 14 and 79 years (mean age, 46.5 years). Their clinical symptoms included coug h, chest pain, and dyspnea. In some patients, the lesions were asympto matic and discovered incidentally on routine chest radiographs. None o f the patients had a previous history of testicular neoplasm or tumor elsewhere. Macroscopically, the tumors were described as soft and tan, with a slightly lobulated cut surface, and measured up to 16 cm in gr eatest dimension. Histologically, the morphologic features were simila r to those of tumors occurring in the gonads, namely, a neoplastic pro liferation of round-to-polygonal cells with indistinct cell borders, c lear-to-lightly-eosinophilic cytoplasm with round-to-oval nuclei and p rominent nucleoli, associated with a prominent inflammatory background composed mainly of mature lymphocytes. Necrosis, hemorrhage, multinuc leated giant cells, granulomatous reaction, and remnants of thymic tis sue were observed in a variable number of cases; mitoses were rare. Im munohistochemical studies in 50 cases showed cytoplasmic staining with placental alkaline phosphatase in 80% of the tumors, focal dotlike po sitivity for CAM 5.2 low-molecular-weight keratins in 75%, focal cytop lasmic staining for wide-spectrum keratin in 70%, focal positive react ion with vimentin in 70%, and focal positivity with HCG in singly scat tered cells in 5%. Immunostains for carcinoembryonic antigen, epitheli al membrane antigen, and alpha-fetoprotein were negative in all the ca ses studied. Fifty patients were Stage I, 3 patients were Stage II, an d 12 patients were Stage III. Clinical followup information was obtain ed for 65 cases (54%). Forty-nine patients were alive and disease free after a period ranging from 1 to 19 years (mean follow-up, 10 years). Sixteen patients died within the same period and were found to have m etastases to distant organs. Of the 16 patients who died, 6 showed ext ension of the tumor outside of the mediastinal compartment at the time of initial diagnosis (Stage III lesions). Aside from clinical staging , the authors' findings also suggest that patients >37 years have wors e outcomes than younger individuals. The authors were unable to find a ny correlation between histopathologic features and clinical behavior in any of these cases. CONCLUSIONS. Clinical and pathologic staging of mediastinal seminomas are important parameters that can be useful in determining the clinical outcomes of patients with these tumors. Tumor invasion into adjacent organs represents a marker of increased morbid ity and mortality. The authors' findings suggest that patients with me diastinal seminomas may have a very good prognosis when the diagnosis is made early; patients with more advanced lesions may require more ag gressive therapy for improved local control and prevention of distant metastases. (C) 1997 American Cancer Society.