Most common Germ cell tumor constituting 50% of all Germ cell tumors.
Age – peak incidence-3rd decade.
Identical tumor in ovary is called dysgerminoma
Genetics– seminoma contain isochromosome 12p & express OCT3/4 and NANOG. Approximately 25% of these tumors have KIT activating mutations. KIT amplifications & KIT over expression is also seen
Morphology:
Grossly-
Seminoma produce bulky masses sometimes ten times the size of the normal testis.
Typical seminoma has a homogenous, gray white lobulated cut surface, usually devoid of hemorrhage or necrosis.
Generally tunica albuginea is not penetrated (rarely epididymis, spermatic cord and scrotal sac extension may occur).
Microscopy:
Typical seminoma is composed of sheets of uniform cells divided into lobules by delicate fibrous septa containing a lymphocyte infiltrate.
Other morphological patterns are
Pseudoglandular
Tubular
Cribriform
Microcystic pattern
Classic seminoma cell is large and round to polyhedral & has a distinct cell membrane, clear or watery appearing cytoplasm,which contains glycogen and large, central nucleus with one or two prominent nucleoli
Mitosis vary in frequency
Some tumours have marked cytologic atypia and mitosis (anaplastic seminoma)
Syncytiotrophoblasts are seen in 15% cases.
Ill defined granulomas may be present
Immunohistochemistry-
Tumor cells stain positively for KIT, OCT 4, SALL4, LIN28 & placental alkaline phosphatise (PLAP).