Human placental lactogen (hPL), also previously known as "human chorionic somatomammotropin", is a 22 kD protein with partial homology to growth hormone. hPL is first detectable in the maternal serum in the fifth week of gestation and reaches a plateau by the thirty-fourth week. hPL has been demonstrated by immunochemistry in the syncytiotrophoblastic cells of choriocarcinoma. A rare variant of trophoblastic tumor has been reported in the testis with resemblance to uterine placental site trophoblastic tumor. It consisted purely of intermediate trophoblasts, which was diffusely positive for hPL and focally for B-hCG.
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