Cyclin D1 is a useful marker for soft tissue Ewing's sarcoma/peripheral Primitive Neuroectodermal Tumor in children and adolescents: A comparative immunohistochemical study with rhabdomyosarcoma.

Cyclin D1 amplification and/or overexpression contribute to the loss of the regulatory circuits that govern G1-S transition phase of the cell cycle, playing pivotal roles in different human malignant tumors, including breast, colon, prostate cancer, lymphoma, melanoma and neuroblastoma. In vitro studies have shown that cyclin D1 is overexpressed in Ewing's sarcoma (EWS)/peripheral Primitive Neuroectodermal Tumor (pPNET), but not in rhabdomyosarcoma cell lines. Only a few immunohistochemical studies are available on cyclin D1 expression in EWS/pPNET, which confirmed its expression only in a limited number of cases. The aim of the present study was a comparative immunohistochemical analysis of the expression and distribution of cyclin D1 in a large series of pediatric/adolescent soft tissue EWS/pPNETs and rhabdomyosarcomas (both embryonal and alveolar subtypes) to assess its potential usefulness in their differential diagnosis. Notably cyclin D1 was strongly and diffusely expressed in all cases (20/20) of EWS/pPNET, while it was lacked in all cases (15/15) of rhabdomyosarcomas. Immunohistochemical overexpression of cyclin D1 in EWS/pPNET is a novel finding which could be exploitable as a diagnostic immunomarker for this tumor. Although highly sensitive, cyclin D1 is not specific for EWS/pPNET, and thus it should not be evaluated alone but in the context of a wide immunohistochemical panel. Accordingly, we first emphasize that when pathologists are dealing with a small round blue cell tumor of soft tissues in pediatric/adolescent patients, a strong and diffuse nuclear expression of cyclin D1 is of complementary diagnostic value to CD99 and FLI-1 in confirming diagnosis of EWS/pPNET and in ruling out rhabdomyosarcoma.

Unclassified pediatric renal stromal tumor overlapping with metanephric stromal tumor and solitary fibrous tumor with diffuse S-100 protein expression.

Metanephric stromal tumor (MST) is a rare pediatric neoplasm unique to the kidneys that is currently included in the spectrum of metanephric tumors, along with metanephric adenoma and adenofibroma. We herein report an unusual case of pediatric renal stromal tumor overlapping with MST and solitary fibrous tumor (SFT). Histologically, the tumor was composed of bland-looking spindle to stellate cells embedded in a fibro-sclerotic stroma that focally surrounded native entrapped renal tubules or blood vessels with abortive rings or collarettes. Alternating hypercellular and hypocellular areas and a focal hemangiopericytomatous-like vascular pattern imparted to the tumor a resemblance to SFT. Angiodysplasia of intratumoral arterioles was also observed, but juxtaglomerular cell hyperplasia was not a feature. Immunohistochemically, the neoplastic cells showed a polyphenotypic profile, including diffuse expression of vimentin and CD34, and focal immunoreactivity for alpha-smooth muscle actin, EMA, and CD99. However, the most striking finding was diffuse nuclear and cytoplasmic expression of S-100 protein. Although this protein has been reported to stain the heterologous glial and/or cartilaginous components that can be occasionally encountered in MST, this marker has not been previously reported in the fibroblastic component of MST. Pathologist should be aware of similar unusual unclassified tumors to avoid potential confusion with other benign or malignant S-100 protein-positive tumors.

Endometrial atypical (bizarre) stromal cells: a potential diagnostic pitfall in biopsy.

Atypical stromal cells (ASCs) may be detected in endometrial polyps and, more rarely, in normal endometrium. Owing to their worrisome cytological features, these cells may represent a potential diagnostic pitfall and are often misinterpreted as malignant, particularly in biopsy samples. We report on ASCs in proliferative phase endometrium of a woman who underwent biopsy for vaginal bleeding. Morphological and immunohistochemical features are discussed in detail. The differential diagnosis to endometrial malignant tumors containing atypical mesenchymal cells is provided.