Background. Malignant germ cell tumors of the mediastinum are unusual, accounting for approximately 10% of all mediastinal tumors. Histologically, the mediastinal seminomas are identical to its gonadal counterpart. We present a rare case of mediastinal seminoma negative for CD117, which is usually positive in most cases.
Case. The patient is a 22 year old male who complained of a chest pain. Further evaluation with computed tomography of the chest revealed an anterior mediastinal mass. Surgical thoracotomy was performed to remove the mediastinal mass and the specimen submitted for histopathologic evaluation. Immunohistochemistry and special stains were performed.
Histopathologic Findings. The mediastinal mass was received fragmented and partly encapsulated. Cut-sections showed tan-yellow, lobulated to nodular cut-surfaces. Microsections revealed a seminomatous lesion. Immunohistochemistry demonstrated a strong positive reaction of the tumor with Placental Alkaline Phospahatase (PLAP). CD117 was occasionally expressed in rare tumor cells while cytokeratin was focal and faint.
Conclusions. Mediastinal seminoma is a rare, distinctive clinicopathologic entity with a wide range of treatment rnodalities. Its diagnosis, even in unusual sites, based on the typical histologic features is paramount given its very favorable prognosis.