Placenta
Gestational trophoblastic diseases
Placental site trophoblastic tumor

Author: Sonali Lanjewar, M.D., MBBS (see Authors page)
Editor: Raavi Gupta, M.D.

Revised: 21 November 2017, last major update November 2017

Copyright: (c) 2003-2017, PathologyOutlines.com, Inc.

PubMed Search: Placental site trophoblastic tumor[title] "loattrfull text"[sb]
Cite this page: Lanjewar, S. Placental site trophoblastic tumor (PSTT). PathologyOutlines.com website. http://pathologyoutlines.com/topic/placentaPSTT.html. Accessed November 22nd, 2017.
Definition / general
  • PSTT, a neoplasm of implantation site intermediate trophoblastic cells, is a rare form of gestational trophoblastic disease (GTD)
    • < 3% of GTD cases
  • Other previously used terms are atypical choriocarcinoma, syncytioma, chorioepitheliosis and trophoblastic pseudotumor
  • Common in reproductive age group (19 - 62 years), typically after a normal pregnancy, spontaneous abortion or hydatidiform mole
  • Most common symptom is vaginal bleeding, however patients may present with amenorrhea, abdominal pain or uterine enlargement
  • Beta-hCG levels are low (< 1,000 mIU/mL)
  • Invasion to ovary and broad ligament can occur
Poor prognostic factors
  • Average age of presentation is 30 years (19 - 62 years)
  • Common presentation is vaginal bleeding, amenorrhea, abdominal pain and uterine enlargement
  • Rarely patient may present with virilization, erythrocytosis and nephrotic syndrome (Obstet Gynecol 1992;79:846, Gynecol Oncol 1999;73:216)
Prognostic factors
    Independent predictors of poorer prognosis are:
  • Advanced FIGO stage
  • Antecedent pregnancy of 48 months or more
  • Presence of tumor cells with clear cytoplasm

Case reports
  • 21 year old woman who died during first pregnancy with primary tubal placental site trophoblastic tumor (Placenta 2011;32:1060)
  • Pregnant woman with with primary tubal placental site trophoblastic tumor (Gynecol Oncol 1999;73:322)
  • Adult man with placental site trophoblastic tumor in a late recurrence of a nonseminomatous germ cell tumor of the testis (Am J Surg Pathol 2004;28:830)
Treatment
  • Curettage or hysterectomy can be curative, however risk of perforation of myometrium is high due to propensity of the tumor to invade the myometrium
  • Approximately 10 - 15% of PSTT are clinically malignant and fail to respond to intensive multiagent chemotherapy
Gross description
  • Tumors are well circumscribed, polypoid extending into the uterine cavity or involve myometrium
  • Cut surface is soft and tan and contains areas of hemorrhage and necrosis
  • Invasion frequently extends to the uterine serosa and, in rare instances, to the adnexal structures including broad ligament (Int J Gynecol Pathol 2003;22:362)
Microscopic (histologic) description
  • PSTT consists of sheets of polygonal to spindle intermediate trophoblastic cells with irregular hyperchromatic nuclei and eosinophilic cytoplasm
    • Tumor cells frequently exhibit marked atypia with large convoluted, hyperchromatic, nuclei and eosinophilic to clear cytoplasm
  • At the periphery, cords or singly scattered tumor cells infiltrate the single muscle fibers of the myometrium
  • Presence of abundant extracellular eosinophilic fibrinoid material and invasion of blood vessels and replacement of the vessel walls of myometrium is a characteristic feature of PSTT
  • Presence of necrosis is indicative of malignant behavior of PSTT
  • Villi are almost never identified
Positive stains
Negative stains
Molecular / cytogenetics description
Differential diagnosis
  • Exaggerated placental site (EPS): the histologic features favoring PSTT over EPS include confluent masses of trophoblastic cells, unequivocal mitotic figures and absence of chorionic villi
  • Choriocarcinoma: comprised of trimorphic proliferation of syncytiotrophoblast, cytotrophoblast and intermediate trophoblast
  • Epithelioid smooth muscle tumors: the distinctive pattern of vascular invasion and the deposition of fibrinoid material favor PSTT
    • Positive staining for HSD3B1, and cytokeratin 18 and negative staining for smooth muscle markers are helpful in this differential diagnosis
  • Epithelioid trophoblastic tumor: ETT grows in expansile nodular fashion in contrast to PSTT where single tumor cells invade and separate single muscle cells
    • Presence of fibrillary hyaline material, extensive geographic necrosis, calcification and absence of vascular invasion favor ETT over PSTT
  • Poorly differentiated carcinoma, metastatic melanoma: distinctive pattern of vascular invasion and the deposition of fibrinoid material including the characteristic positive immunostains above favors PSTT
Board review question #1
    Characteristic histological features helpful in differentiating PSTT from most other neoplasms are:

  1. Ability to replace and reepithelialize the endocervical / endometrial surface epithelium.
  2. Atypical hyperchromatic nuclei with atypical mitosis.
  3. Invasion and replacement of vessel wall of myometrium.
  4. Presence of geographic necrosis.
Board review answer #1
C. Invasion and replacement of vessel wall of myometrium.