Placenta - Placental site trophoblastic tumor (PSTT)

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Placenta

Gestational trophoblastic disease

Placental site trophoblastic tumor (PSTT)

Reviewers: Mandolin Ziadie, M.D. (see Reviewers page)
Revised: 10 December 2011, last major update December 2011
Copyright: (c) 2003-2011, PathologyOutlines.com, Inc.

Definition
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● Rare, usually benign tumor also known as atypical choriocarcinoma, trophoblastic pseudotumor
● Attributed to neoplastic transformation of implantation-site intermediate trophoblast
● 2 malignant cases reported at (Am J Surg Pathol 1993;17:1003)
● Occurs in reproductive age women (occasionally age 50+); 75% occur long after normal pregnancy, 5% follow molar pregnancy
● Patients present with amenorrhea or abnormal bleeding with enlarged uterus and persistently elevated serum hCG
● Rarely associated with virilization
● Associated with distinctive renal glomerular lesion (occlusive eosinophilic deposits in glomerular capillary lumina) accompanied by proteinuria and hematura (Hum Pathol 1985;16:35)

Poor prognostic factors
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● 5+ mitotic figures / 10 HPF
● Ki-67 > 50%
● High cellularity
● Extensive necrosis
● Preponderance of cells with clear cytoplasm and atypical nuclei
● Metastasis / local spread

Treatment
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● Curettage or hysterectomy
● Monitor hCG, may be resistant to chemotherapy
● 10% mortality due to metastases to lungs, liver, abdominal cavity and brain

Gross description
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● Soft myometrial mass projecting into uterine cavity or intramural; may perforate uterus
● May only be microscopic
● Ill defined or localized, may have hemorrhage or necrosis

Micro description
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● Intermediate trophoblast proliferation (medium spindled or polyhedral mononuclear cells with irregular borders) that deeply invade myometrium in large nests, interdigitating pattern or masses
● No cytotrophoblast, no villi
● Extensive deposition of fibrinoid material
● Invasion of blood vessels with fibrinoid deposition

Positive stains
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● hCG (multinucleate cells only), HLA-G, hPL, Keratin
● Ki-67 (> 10%), Mel-CAM

Negative stains
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● PLAP

Molecular description
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● Diploid

EM description
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● Prominent paranuclear filaments not present in intermediate trophoblasts of choriocarcinoma (Hum Pathol 1989;20:370)

Differential diagnosis
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● Epithelioid leiomyoma, leiomyosarcoma: lack distinctive feature of vascular invasion with fibrinoid deposition of placental site trophoblastic tumor, hPL-, inhibin-alpha negative, desmin+ and actin+; sarcomas are keratin negative
● Invasive mole: villi are present
● Choriocarcinoma: has dimorphic population of cytotrophoblast and syncytiotrophoblasts, hemorrhage and infiltration

Benign lesions:
● Exaggerated placental site reaction: non-neoplastic proliferations of trophoblast
● Placental site nodules: well circumscribed, tend to be extensively hyalinized, minimal mitotic activity, may have Mallory bodies, small and circumscribed

End of Placenta > Gestational trophoblastic disease > Placental site trophoblastic tumor (PSTT)

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