**Core Concept**
Placental site trophoblastic disease (PSTT) is a rare, malignant gestational trophoblastic disease that originates from the placental bed. It is characterized by the proliferation of intermediate trophoblastic cells, which invade the myometrium.

**Why the Correct Answer is Right**
The treatment of choice for PSTT is surgical excision, specifically hysterectomy, due to its potential for local invasion and recurrence. This approach allows for complete removal of the tumor and prevents further complications. The use of chemotherapy may be considered in cases of incomplete resection or metastatic disease.

**Why Each Wrong Option is Incorrect**
**Option A:** Chemotherapy alone is not sufficient for the treatment of PSTT, as it may not address the local invasion of the tumor.
**Option B:** Radiation therapy is not typically used for PSTT, as it is not effective in treating the invasive nature of the disease.
**Option C:** Expectant management is not appropriate for PSTT, as it can lead to progression and metastasis.

**Clinical Pearl / High-Yield Fact**
PSTT is often associated with a higher risk of local recurrence and metastasis compared to other gestational trophoblastic diseases, emphasizing the importance of complete surgical excision.

**Correct Answer: D. Hysterectomy.**