Choriocarcinoma : Microscopic Features
Choriocarcinoma has a distinctive biphasic appearance consisting of mononucleated trophoblastic cells closely associated with and capped by multinucleated syncytiotrophoblasts in a hemorrhagic background. The tumor cells form plexiform aggregates and structures reminiscent of early placental villi without stromal cores. The mononucleated trophoblastic cells include numerous smaller cytotrophoblasts and scant numbers of larger intermediate trophoblasts. The cytotrophoblasts have clear or light pink cytoplasm, distinct cell borders, irregular nuclei, prominent nucleoli, and brisk mitotic activity. The syncytiotrophoblasts are large cells with abundant deeply eosinophilic cytoplasm and one or more nuclei with dark, smudgy chromatin. They have spindle or elongated cytoplasmic extensions that surround clusters of cytotrophoblasts or percolate within them.