Intense immunoreactivity with placental alkaline phosphatase (PLAP) in a seminoma. The staining pattern is mostly membranous with some cytoplasmic staining. PLAP is a very sensitive marker for germ cell tumors (positive in > 95% of seminomas) but it lacks specificity. It is frequently expressed in gastrointestinal, gynecologic, breast, lung, and urologic cancers. In addition to PLAP, seminomas show immunoreactivity for CD117 (c-kit), OCT3/4 (a transcription factor expressed in embryonic stem cells and germ cells), and SALL4. Seminomas are usually negative for CD30, EMA, and high molecular weight keratin.