The presence of mitotic figures was investigated in 215 cases of florid atypical endometrial change associated with chorionic tissue effect. Mitoses were found in 13.4% of the cases. Mitoses were occasionally observed in 10.2% of cases, and they were multiple in single microscopic fields in 2.7%. Abnormal mitoses were noted in 3.2% of the cases. The occurrence of normal and abnormal mitoses was mainly related to the early secretory type of abnormality. These observations have biologic implications, but of more practical interest, they indicate that the presence of mitoses per se are an insufficient criteria for the diagnosis of clear-cell carcinoma, particularly in women during their reproductive period.

Erdheim-Chester disease (ECD) is a rare, xanthogranulomatous, non-Langerhans cell histiocytosis with frequent systemic involvement. Although the diagnosis is based on characteristic histological and radiological findings, its identification can be challenging because of its heterogeneous presentation. Osteosclerosis of long bones, often associated with bone pain, is the most common initial manifestation, followed by extraskeletal manifestations in approximately 50% of cases. There is no standard treatment for ECD, although recommendations have been made on the basis of small studies. A systematic approach to the diagnosis of ECD is important, because its manifestations may be life-threatening and may require specific management. We report an atypical presentation of ECD, with early cardiac, renal, and central nervous system involvement, and only late skeletal manifestations.

Rhabdomyosarcomas (RMS) are malignant mesenchymal tumors with skeletal muscle differentiation which are classified into alveolar, embryonal, pleomorphic, and spindle cell/sclerosing RMS. Within the spindle cell/sclerosing RMS tumor type there is a recently recognized sub-type categorized as intraosseous spindle cell RMS with TFCP2/NCOA2 gene fusion. This rare tumor is highly aggressive with predominant involvement of the craniofacial and pelvic bones with approximately 30 cases reported to date. Histopathologic features include spindle cell and epithelioid morphology with a characteristic co-expression of epithelial markers, myogenic markers, and ALK1 expression. We report two cases of gnathic spindle cell/sclerosing RMS with FUS::TFCP2 gene fusion that were initially interpreted as carcinomas by referring institutions and later reclassified when encountered in our practice after additional work-up and molecular characterization.