Objective Histologic Characterization of Trophoblastic Proliferations

Abstract

Abstract Introduction/Objective Placental site nodules (PSNs) are rare intermediate trophoblastic lesions characterized by hyalinized cellular aggregates that are small, well-circumscribed, non-necrotic, and paucicellular. PSNs are generally incidental in gynecologic specimens. ETTs are malignant proliferations of intermediate trophoblasts and are generally larger, with nuclear atypia, and higher mitotic rate. Atypical placental site nodules (APSNs) are histologically intermediate between PSN and ETT and not well characterized in the literature to date. There exists room for more objective characterization of PSN and APSN. We use objective measurements to characterize trophoblastic proliferations based on size, location, mitotic rate, number of trophoblasts per high-power field (t-HPF), ki-67 index, beta-hCG, time since last pregnancy, presence of calcification or necrosis, and clinical follow-up. Methods The surgical pathology database of a single large academic institution was searched for cases of “placental site nodule,” “atypical placental site nodule,” “epithelioid trophoblastic tumor,” and “placental site trophoblastic tumor”. Clinical and morphologic data were recorded for each case. Ki-67/cytokeratin AE1/AE3 dual immunohistochemical stains were performed to assess the proliferative index of the trophoblastic cells. Results 70 cases of trophoblastic lesions (53 PSN, 4 APSN, 5 ETT, 8 PSTT) were identified. Results include: PSNs were on average 3.2 mm, 56.5 t-HPF, and 2.6% ki-67. APSNs 4.3 mm, 97.8 t-HPF, and 6.4% ki-67. ETTs 16.5 mm, 161.8 t-HPF, and 12.2% ki-67. Conclusion Objective measurements of trophoblastic lesions, as well as correlation with clinical data, may be useful for more accurate classification of these lesions, especially by those who encounter them rarely. To date, the clinical risk, optimal management, and risk for progression of APSNs are not well characterized and thus are worthy of additional study and description. For example, in our data, 14 cases originally signed out at PSN were at least 4 mm, which may re-classify them as APSN.