Path Image
The neoplastic intermediate trophoblasts exhibit prominent nuclear pleomorphism.

The neoplastic intermediate trophoblastic cells are polygonal with prominent nuclear pleomorphism. Note the infiltrative growth into the myometrium.

Another case demonstrates the infiltrative nature of the neoplastic intermediate trophoblasts. They are interdigitating with the muscle fascicles of the myometrium.

The cytoplasm of the intermediate trophoblastic cells may occasionally be vacuolated. They may also appear spindled, especially in areas of myometrial invasion.

Another case demonstrates the marked cytologic atypia of the neoplastic cells, which are dissecting between smooth muscle fibers.

Yet another example, which illustrates a mitotic figure (arrow).


Placental site trophoblastic tumor (PSTT) are rare and account for less than 2% of gestational trophoblastic neoplasms. PSTTs are preceded by a normal pregnancy in one-half of cases, followed by a spontaneous abortion (one-sixth) or a molar pregnancy (one-fifth). PSTT arise from intermediate trophoblasts which form the implantation site. They are mononuclear cells with abundant cytoplasm and are weakly reactive for human placental lactogen.1

Microscopically, PSTT is composed of atypical intermediate trophoblasts that dissect through the smooth muscle fibers of the myometrium. Areas of necrosis and fibrinoid deposition are common. Furthermore, a peculiar characteristic of this tumor is that the neoplastic cells often replace the walls of blood vessels while preserving their lumens.

It may be difficult to distinguish PSTT from exaggerated placental implantation site. Therefore, use of Ki-67 may be helpful and it is abnormally increased in PSTT. Furthermore, areas of necrosis are often seen in PSTT, but not in placental implantation sites.


Typically presents as irregular vaginal bleeding with a low serum hCG. In addition, patients are usually positive for human placental lactogen. Compared to choriocarcinoma which follows a pregnancy by only weeks or months, PSTT may present several years after the pregnancy. Furthermore, 50% of choriocarcinomas follow a molar pregnancy, and in contrast, most cases of PSTT follow a normal pregnancy.3


While some patients may be cured with a dilation and curettage, optimal therapy consists of a hysterectomy. These tumors are locally invasive and rarely metastasize. When metastases are present, patients may be treated with the same chemotherapy regimens as choriocarcinoma.


If the diagnosis is made within two years from the pregnancy, the neoplasm is usually localized (stage I or II) and outcome is good. However, if the tumor is diagnosed 4+ years after pregnancy, chances are the disease is advanced with a poor prognosis. Overall, 10-15% of cases result in metastases and death.1,2


Placenta : Exaggerated Placental Site

Placenta : Gestational Choriocarcinoma

Endometrium : Placental Site Nodule


1 Kumar V, Abbas AK, Fausto N. Robbins and Cotran Pathologic Basis of Disease. 7th Ed. Philadelphia, PA: Elsevier; 2005: 1114.

2 Mazur MT, Kurman RJ. Diagnosis of Endometrial Biopsies and Curettings. New York, NY: Springer; 2005: 85-91.

3 Fletcher CDM, ed. Diagnostic Histopathology of Tumors. 3rd Ed. Philadelphia, PA: Elsevier; 2007: 679-80.

Last updated: 2010-10-26
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