Placental site nodule

PSTT, and Ki-67 labeling of less than 8% to 10% favors placental site nodule over ETT. 

Placental site nodules are composed of mitotically inactive intermediate trophoblastic cells of chorionic type within a nodular, hyalinized stroma. Lesional cells express pan-trophoblastic markers as well as the chorionic intermediate trophoblast-associated markers FLAP and p63. The Ki-67 index in a placental site nodule is less than 10% to 15% ... 

This tumor is composed of neoplastic implantation site intermediate trophoblasts that inhltrate myometrium. hPL and HLA-G are typically expressed. Placental site trophoblastic tumors have an index of 14% (+/- 7%) PSTTs can also contain scattered hCG-expressing syn-cytiotrophoblasts, but they are rare and haphazardly situated, not intimately admixed with mononuclear trophoblasts as is typical of choriocarcinoma. Biopsy or curettage material may suggest the presence of PSTT or placental site nodule. Both the immunophenotype and proliferative index of these lesions differ, with preferential expression of hPL and HLA-G in PSTT, as opposed to FLAP and p63 in placental site nodule. 749... 

Huettner PC, Gersell DJ. Placental site nodule A clinicopathologic study of 38 cases. Int J Gynecol Pathol. 1994 13 191-198. 

Shih IM, Seidman JD, Kurman RJ. Placental site nodule and characterization of distinctive types of intermediate trophoblast. Hum Pathol. 1999 30 687-694. 

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