Although PSN is classified as a benign gestational trophoblastic disease, atypical PSN (aPSN: higher cell count, nuclear atypia, mitotic activity, and Ki-67 proliferation index compared to PSN) has been suggested as being associated with trophoblastic malignancy [10,11]. PSNs may also be histologically confused with squamous cell carcinoma of the cervix; however, PSNs are immunoreactive for inhibin-α and cytokeratin-18, whereas squamous cell carcinomas are negative [5]. Here, KRT18 is linked to squamous cell carcinoma.