Background: Placental site trophoblastic tumor (PSTT) is a rare form of trophoblastic neoplasm. Approximately 100 cases of PSTT have been reported, but we found no report on its cytodiagnosis.
Cases: Case 1, a 39-year-old female, came to the hospital because of abnormal genital bleeding. Case 2, a 36-year-old female came because of amenorrhea for a year. In both cases, endometrial smear and intrauterine curettage suggested trophoblastic disease, and hysterectomy was performed. Laboratory data revealed a mild increase in human chorionic gonadotropin (hCG) and beta-hCG but normal human placental lactogen (hPL). In the cytologic examination, the background contained some hemorrhagic and fibrinous areas but no necrosis. Most tumor cells stained light green, were round or polygonal, and contained abundant cytoplasm. Some were palely stained and had vacuoles. Some cells showed hyperchromatism, an irregular nucleus, fine-to-coarse chromatin granules and markedly different sizes. Most of the cells were hPL positive, and a few were hCG positive.
Conclusion: Both cases were considered benign because of rare mitoses despite cellular pleomorphism. However, careful follow-up is required. The differential diagnosis of PSTT is difficult from cytologic and biopsy specimens alone but may be achieved with additional magnetic resonance imaging findings and positive staining of hPL and hCG.