Placental site trophoblastic tumor (PSTT) is a rare and unique type of gestational trophoblastic tumor originating from the placental implantation site. It accounts for approximately 1%–2% of gestational trophoblastic tumors. In most cases, the tumor does not metastasize and has a favorable prognosis. However, in cases with metastases, the prognosis is poor.
Pathology
Macroscopically, the tumor can appear as polypoid tissue projecting into the uterine cavity or may invade the uterine myometrium and spread beyond the uterus. The cut surface is typically yellow-brown or yellow. Microscopically, the tumor is almost entirely composed of intermediate trophoblastic cells from the implantation site, lacking any villous structures. It infiltrates in single or sheet-like patterns between the uterine muscle fibers, and the tumor cells can entirely replace the walls of muscle layer vessels, which is considered characteristic. Immunohistochemical staining typically shows diffuse expression of implantation-site trophoblastic markers such as human placental lactogen (hPL) and CD146.
Clinical Features
PSTT predominantly occurs during the reproductive years and is rare after menopause. The average age of onset is 31–35 years. It often follows term delivery, miscarriage, or hydatidiform mole, although the latter is relatively rare. It occasionally coexists with a viable pregnancy. Common symptoms include irregular vaginal bleeding or heavy menstrual bleeding after an episode of amenorrhea. On physical examination, the uterus may appear uniformly or irregularly enlarged. Only a small number of cases exhibit extrauterine metastases, with common sites of involvement including the lungs, vagina, brain, liver, kidneys, and pelvic or para-aortic lymph nodes. When metastases occur, the prognosis is generally poor.
Diagnosis
Due to nonspecific symptoms and signs, PSTT is prone to misdiagnosis. Definitive diagnosis relies on histological analysis, which can be achieved through curettage specimens, though in most cases, an accurate diagnosis is made using the uterine specimen obtained via surgery. The following auxiliary investigations are commonly used.
- Serum hCG Measurement: The levels are mostly negative or mildly elevated and do not correlate with tumor burden, making it unhelpful for prognostic evaluation.
- hPL Measurement: Serum hPL levels are typically mildly elevated or negative, although immunohistochemical staining is usually positive.
- Ultrasound Examination: The findings are often similar to those of uterine fibroids or other trophoblastic tumors. Color Doppler ultrasound may reveal abundant uterine blood flow.
Clinical Staging and High-Risk Factors
The anatomical staging from the FIGO staging system is applicable, but the prognostic scoring system is not. Factors considered high-risk for poor prognosis in PSTT include:
- Deep myometrial invasion, extensive necrosis, mitotic count >5/10 high-power fields (HPF), and lymphovascular space invasion.
- An interval of more than two years since the preceding pregnancy.
- Extrauterine metastases.
Treatment
Surgery is the preferred treatment. In patients with non-metastatic PSTT (Stage I), total hysterectomy with bilateral salpingectomy is performed. For those with retroperitoneal lymphadenopathy indicated on imaging, lymph node biopsy is necessary. Postoperative chemotherapy should be considered for patients who are found to have one or more poor prognostic factors.
For patients with metastatic PSTT, the treatment involves total hysterectomy with bilateral salpingectomy, maximum resection of metastatic lesions, and chemotherapy, with EP/EMA regimens as the preferred choice.
For young patients who wish to preserve fertility and have Stage I disease with localized lesions, local resection of the lesion may be performed via hysteroscopy, laparoscopy, or abdominal approaches, followed by chemotherapy. However, there is a lack of large-scale clinical data supporting this treatment, so it is not routinely recommended.
Follow-Up
Follow-up is necessary after treatment and is similar to the follow-up for gestational trophoblastic tumors. Since serum hCG levels are mostly normal or only mildly elevated in PSTT, clinical symptoms and imaging findings are more valuable for monitoring during follow-up.