Endometrium, Placental site nodule

Often an incidental finding on endometrial biopsies or endocervical curettages, placental site nodules are benign placental remnants originating from chorionic laeve. These lesions derive from chorionic-type intermediate trophoblast and are composed of nodular aggregates of non-atypical eosinophilic cells in a hyalinized stroma. Peripheral chronic inflammation is usually present.

Due to the epithelial nature of chorionic type intermediate trophoblast, these lesions stain positively for p63. The percentage of cells staining with MIB1 is usually less than 8%.

The malignant counterpart to this lesion is the epithelioid trophoblastic tumor (ETT) for which squamous cell carcinoma also comes into the differential diagnosis.