A placental site trophoblastic tumor (PSTT) is a rare form of gestational trophoblastic disease. These tumors arise from placental cells left behind after any pregnancy, such as a full-term delivery, miscarriage, or abortion. PSTT is a unique cancer derived from pregnancy-related tissue, with an incidence of approximately 1 in 100,000 pregnancies.
What is a Placental Site Trophoblastic Tumor?
A PSTT is a malignant tumor originating from intermediate trophoblasts, specialized cells found where the placenta implants in the uterus. These tumors can appear months or even years after any pregnancy. PSTTs are distinct from other gestational trophoblastic diseases due to their slower growth rate.
Unlike other gestational trophoblastic diseases that produce high levels of human chorionic gonadotropin (hCG), PSTTs typically produce lower amounts of hCG. Instead, these tumors are more likely to secrete human placental lactogen (hPL), which can be a distinguishing hormonal marker. This difference in hormone production can make PSTT diagnosis more challenging.
The tumor cells often infiltrate the myometrium, the muscular wall of the uterus, and can extend to its outer surface. While often confined to the uterus in early stages, PSTTs have the potential to spread to other parts of the body.
Identifying Symptoms and Diagnosis
The most common symptom associated with PSTT is irregular vaginal bleeding, which can occur months or even years after a pregnancy. Some individuals may also experience amenorrhea, the absence of menstruation. Symptoms can also include abdominal pain or those related to the tumor’s size, or even symptoms from spread to distant organs like the lungs or brain.
Diagnosis begins with a physical examination and blood tests. These tests specifically look for levels of human placental lactogen (hPL) and human chorionic gonadotropin (hCG). While hCG levels may be slightly elevated in PSTT, they are typically much lower than those seen in other gestational trophoblastic diseases like choriocarcinoma, where hCG levels can be significantly higher.
Imaging studies assess the tumor’s size and potential spread. Ultrasound can identify an echogenic and vascular mass within the endometrium or myometrium. Magnetic resonance imaging (MRI) may show a heterogeneous mass in the endometrial and myometrial areas with disrupted junctional zones, often containing cystic spaces and vascular structures. Computed tomography (CT) scans are primarily used to detect if the disease has spread to other parts of the body.
A definitive diagnosis of PSTT generally requires a biopsy and subsequent pathological examination of tissue. Immunohistochemical staining is often performed on the biopsy sample, which can show strong positivity for hPL and keratin, helping to differentiate PSTT from other forms of gestational trophoblastic neoplasia. This analysis helps confirm the presence of intermediate trophoblast cells and their malignant potential.
Treatment Options
Surgery is the primary treatment for PSTT, especially when the tumor is confined to the uterus. A hysterectomy, the surgical removal of the uterus, is considered the cornerstone of treatment due to the tumor’s typical resistance to chemotherapy. This approach is highly effective for localized disease.
Chemotherapy may be considered when the disease has spread beyond the uterus or if there is a recurrence. PSTTs are known for their relative resistance to chemotherapy compared to other types of gestational trophoblastic disease. Combination chemotherapy regimens may be used in these more advanced or resistant cases.
A multidisciplinary team approach is often employed in managing PSTT, involving specialists from various medical fields. This collaborative care helps to develop an individualized treatment plan. For instance, if the interval from the antecedent pregnancy is greater than four years, or if there is deep myometrial invasion, adjuvant chemotherapy might be recommended after surgery.
Life After Treatment and Outlook
The prognosis for individuals with PSTT is generally favorable, particularly when the disease is confined to the uterus and treated promptly with surgery. For stage I disease, the 10-year overall survival rate can be as high as 90% or even 100%. However, if the disease has spread to other stages, the prognosis can be less favorable, with a 10-year overall survival rate for stage II, III, and IV disease around 49-52%.
Long-term follow-up and monitoring are important to detect any potential recurrence early. This involves regular physical examinations, blood tests to monitor hPL and hCG levels, and imaging studies. While hCG levels may not be a reliable indicator of tumor burden in PSTT, their monitoring can still be part of the follow-up protocol.
For individuals who wish to preserve fertility, hysterectomy, as the primary treatment, often means that fertility cannot be maintained. However, in select cases of localized disease, fertility-sparing surgical approaches might be explored, though these are less common due to the infiltrative nature of PSTT. The decision regarding fertility preservation is made on an individualized basis, considering the extent of the disease and patient preferences.