Placenta
Gestational trophoblastic diseases
Placental site trophoblastic tumor (PSTT)

Author: Sonali Lanjewar, M.D., MBBS (see Authors page)
Editor: Raavi Gupta, M.D.
Editorial Board Member Review: Carlos Parra-Herran, M.D.

Revised: 19 December 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://www.pathologyoutlines.com/topic/placentaPSTT.html. Accessed August 18th, 2018.
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 (average age 30 - 32 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
Clinical features
Prognostic factors
    Independent predictors of poorer prognosis are (Lancet 2009;374:48):
  • 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 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
  • Hysterectomy is curative in most patients; however risk of perforation of myometrium is high due to propensity of the tumor to invade the myometrium
  • 25 - 30% of patients develop recurrence; 15% die of disease (Gynecol Oncol 2001;82:415, J Reprod Med 2002;47:460)
  • Approximately 10 - 15% of PSTT are clinically malignant and fail to respond to intensive multiagent chemotherapy
Gross description
  • Tumors can be polypoid extending into the uterine cavity or display endophytic myometrial growth
  • 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 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 not identified, unless the index gestation was recent (weeks); in this case other possibilities need to be excluded first (exaggerated implantation site, invasive mole)
Positive stains
Negative stains
Molecular / cytogenetics description
Differential diagnosis
  • Choriocarcinoma: comprised of trimorphic proliferation of syncytiotrophoblast, cytotrophoblast and intermediate trophoblast; strong and diffuse bHCG expression; markedly elevated serum bHCG
  • 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
    • Positive p63 and inhibin favor ETT (which originates in chorionic leave intermediate trophoblast)
  • Exaggerated placental site (EPS): the histologic features favoring PSTT over EPS include remote (rather than recent) prior pregnancy, confluent trophoblastic cells, unequivocal mitotic figures and necrosis
  • Malignant melanoma: distinct, large nucleoli should raise this possibility; unlike melanoma, PSTT has strong predilection for myometrial vessels and is negative for melanoma markers (HMB45, MelanA, S100)
  • Molar gestation (complete mole, invasive mole): presence of abnormal chorionic villi; extravillous trophoblast is atypical but usually less abundant than in PSTT
  • Poorly differentiated endometrial carcinoma: glandular differentiation (albeit focal), variant differentiation (squamous, tubal); conversely, involvement of vessel walls, deposition of fibrinoid material and expression of hPL / Mel-CAM favors PSTT; both can express cytokeratins
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. Invasion and replacement of myometrial vessel walls
  3. Presence of distinct neoplastic components (triphasic tumor)
  4. Presence of extensive geographic necrosis and expression of p63
Board review answer #1
B. Invasion and replacement of myometrial vessel walls