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Sclerosing epithelioid fibrosarcoma (SEF) is a rare fibrosarcoma variant with specific histomorphology and consistent translocation (EWSR1-CREB3L1/2). To date, 110 cases have been reported; only 15 originated within the abdomen. With only 2 cases reported parallel to our study and one case briefly mentioned in a previous series, primary renal SEF is exceptionally rare but might be underrecognized. We herein describe 2 cases affecting a 23-year-old woman and a 43-year-old man. Tumor size was 22 and 4.2 cm, respectively. Patient 1 developed skeletal and multiple pulmonary metastases. She died of disease 82 months later, despite aggressive multimodality therapy. Patient 2 has no evidence of recurrence or metastasis (8 months after surgery). Histologic examination showed similar appearance with monotonous bland medium-sized epithelioid cells with rounded slightly vesicular nuclei and clear cytoplasm imparting a carcinoma-like appearance set within a highly sclerotic hyaline fibrous stroma. The tumor cells were arranged in nests, single cell cords, trabeculae, or solid sheets with frequent entrapment of renal tubules and glomeruli. Immunohistochemistry showed strong expression of vimentin, bcl2, CD99, and MUC4, whereas cytokeratin and other markers were negative. Fluorescence in situ hybridization showed a translocation involving the EWSR1 gene locus in case 2. Molecular analysis in case 1 was not successful due to poor signal quality. To our knowledge, this is the second report documenting primary renal SEF. Awareness of this entity would help avoid misinterpretation as clear cell carcinoma, sclerosing perivascular epithelioid cell tumor, Xp.11 translocation carcinoma, and other more frequent neoplasms at this site., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Histologic changes of regression have been recognized in many malignant tumors, although they have not been documented in thyroid carcinoma. We analyze here the histologic features of 2 cases of papillary thyroid microcarcinoma, one of the diffuse sclerosing variant and another multicentric of the follicular variant, that suggest partial regression. The histologic and clinical features of the 2 thyroid microcarcinomas were compared with the features of regression reported in other tumors. Hematoxylin and eosin stains were examined in each case. In addition, immunoperoxidase stains for thyroglobulin and thyroid transcription factor-1 were performed on the metastatic and primary lesions of each case. Immunostains for CD4 and CD8 performed on the thyroid lesions were also examined. Both patients presented with metastatic papillary thyroid carcinoma in regional lymph nodes with no clinical or radiologic evidence of primary tumor in the thyroid glands. When examined, the thyroid glands revealed only microscopic foci of papillary thyroid carcinoma measuring less than 1.5 mm, diffuse sclerosis and a lymphocytic infiltrate mainly composed of cytotoxic T lymphocytes around the neoplastic microfollicles. Numerous psammoma bodies were also found in the thyroid of case 1, and venulitis similar to that seen in acute hepatic rejection was also seen in the microcarcinoma of case 2. The 2 patients reported had papillary thyroid microcarcinomas measuring less than 1.5 mm and features suggestive of regression characterized by extensive fibrosis, an accompanying T lymphocyte infiltrate, venulitis, and only a few clusters of neoplastic cells or a few neoplastic follicles. Thus, we believe that these histologic changes suggest regression because papillary thyroid microcarcinomas measuring less than 1.5 mm do not metastasize and have been considered innocuous or medical curiosities.

A 73-year-old woman presented with abdominal pain, weakness, and weight loss. Pertinent medical history included myelofibrosis, severe anemia, and lumpectomy for breast cancer. Computed tomography showed marked splenomegaly and numerous soft tissue masses in the mesentery. Excisional biopsy of the mass showed an encapsulated tumor with yellow-tan nodular growth pattern. Microscopically, the tumor was characterized by the presence of bizarre giant cells in background of prominent dense fibrous stroma. The atypical giant cells were positive for FVIII antibody staining. Many other cells were positive for CD43 antibody staining, indicating that the tumor was hematopoietic in nature, so-called sclerosing extramedullary hematopoietic tumor. Extramedullary hematopoiesis is a common phenomenon associated with severe anemia of any cause. When associated with myelofibrosis, however, it has different morphology from extramedullary hematopoiesis of the other causes. The significance of recognizing sclerosing extramedullary hematopoietic tumor is that it is often mistaken for sarcomas and other malignant neoplasms, especially when the clinical history is unknown., (Copyright 2002, Elsevier Science (USA). All rights reserved.)