Mallory's bodies in placental site nodule

We report two cases of placental site nodule in which Mallory's bodies were found in the intermediate trophoblasts constituting the lesion. Mallory's bodies are known to occur in hepatocytes and pulmonary alveolar cells in a wide variety of conditions, and represent abnormal cytoplasmic aggregates of cytokeratin intermediate filaments. Their occurrence outside the liver and lung is exceptional. In the present cases, they were immunoreactive for both low- and high-molecular-weight cytokeratins. Since high-molecular-weight cytokeratin is not normally expressed in intermediate trophoblasts, the formation of Mallory's bodies appears to involve aberrant expression of cytoskeletal proteins.