Reactivity with TdT in Merkel cell carcinoma: a potential diagnostic pitfall

Merkel cell carcinoma (MCC) is a high-grade neuroendocrine carcinoma of skin characterized by cells with a "blastic" appearance, scant cytoplasm, and fine, evenly distributed chromatin. Terminal deoxynucleotidyl transferase (TdT) is a DNA polymerase present in thymic T cells, lymphoblastic lymphoma/leukemia, and some cases of acute myeloid leukemia. After observing TdT immunoreactivity in a case of MCC, we analyzed 26 tumors by immunohistochemical analysis to determine their spectrum of reactivity with TdT and identified TdT in 19 (73%) of 26 MCCs. Staining intensity was variable but was often moderate to strong and present in a significant percentage of cells. Because MCC has cytomorphologic features similar to those of lymphoblastic lymphoma and may manifest as metastatic disease, reactivity with TdT in MCC could represent a diagnostic pitfall in the differential diagnosis with lymphoblastic lymphoma, particularly because the latter may lack CD45 and/or CD20, yet both neoplasms may express PAX-5, a B-cell-associated marker.     

Desmin expression in spindle cell lipomas: a potential diagnostic pitfall

The immunohistochemical analysis of the spindle cell lipomas has been for the most part limited to the study of S-100 protein, CD34, and Bcl-2 reactivity. To evaluate the immunoexpression of desmin and actins in spindle cell lipomas of different histological subtypes a retrospective immunohistochemical study of 25 spindle cell lipomas using archival formalin-fixed, paraffin-embedded tissue was performed. Strong positivity of the spindle cell component for desmin was found in 4 of 25 cases (16%). The expression was diffuse in two cases and focal (in up to 25% of the spindle cells) in the other two. Two of these cases were of the classical type and the other two were angiomatous spindle cell lipomas. Desmin-positive and desmin-negative spindle cells showed no morphological differences. The spindle cell component expressed CD34 in all cases and Bcl-2 in 14 of the 25 cases. There was no immunoreactivity for smooth muscle actin, muscle-specific actin, or S-100 protein. We conclude that a significant proportion of spindle cell lipomas express desmin, and therefore that the immunoreactivity for this antigen does not exclude the diagnosis, even in lesions with nonclassical histological features and/or atypical locations.     

Sporadic renal hemangioblastoma with CA9, PAX2 and PAX8 expression: diagnostic pitfall in the differential diagnosis from clear cell renal cell carcinoma

To date, 13 cases of sporadic renal hemangioblastoma have been reported. In this article, we report such a case that might cause the diagnostic pitfall. A 37-year-old Japanese was found to have a renal mass by periodic medical check-up. He underwent radical nephrectomy. Macroscopically, the tumor was well-defined without fibrous capsule and the cut surface of the tumor exhibited light brown to gray-tan color without hemorrhage or necrosis. Microscopically, the tumor was made up of large polygonal to short spindle cells with eosinophilic cytoplasm with occasional vacuolization and abundant arborizing capillary network. Immunohistochemically, neoplastic cells showed diffuse positivity for inhibin-alpha, S-100 protein, vimentin, CA9, PAX2 and PAX8, but negativity for cytokeratin CAM5.2, alpha smooth muscle actin, Melanosome, Melan A, TFE3 and cathepsin K. In genetic analyses, this tumor showed no changes of VHL gene mutation, hypermethylation and loss of heterozygosity of chromosome 3p. Additionally, G-band karyotype and array comparative genomic hybridization studies showed a normal chromosome. In conclusion, the positivity for CA9, PAX2 and PAX8 in sporadic renal hemangioblastoma may cause the critical diagnostic pitfall in the differential diagnosis from clear cell renal cell carcinoma. Pathologists need to pay attention to systemic evaluation including macroscopic, microscopic and immunohistochemical findings. In some cases, molecular genetic study may be necessary.     

Retrieved endogenous biotin: a novel marker and a potential pitfall in diagnostic immunohistochemistry

 

Aim:

Antigen retrieval (AR) procedures are based on the effect of heating (by either microwave or pressure cooking treatments) on routinely fixed and paraffin embedded tissues. We observed that AR procedures restore the reactivity of endogenous biotin (EB) and report on the distribution of EB following AR in a series of routinely fixed and embedded tissues.  

Methods and results:

Following pressure cooking or microwave treatments, a simple streptavidin–peroxidase staining revealed retrieved endogenous biotin (REB) in normal tissues (such as liver, kidney and adrenal cortex), in oxyphylic cells and in some tumours, especially in carcinomas of the kidney and of the adrenal cortex. In formalin-fixed (but not in alcohol-fixed) tissue sections, the heating procedures caused an intense and finely granular cytoplasmic reaction, following a routine streptavidin-conjugated peroxidase treatment. The staining was prevented by blocking of EB by a sequential avidin–biotin treatment.  

Conclusions:

Retrieval of EB reactivity can cause pitfalls in diagnostic immunohistochemistry but, alternatively, it might also constitute a useful and novel diagnostic marker.     

Sertoliform endometrioid carcinoma of the ovary: a potential diagnostic pitfall

Sertoliform endometrioid carcinoma of the ovary (SEC) is an uncommon variant that bears histologic similarity to Sertoli and Sertoli-Leydig cell tumors (SLTs). Clinically, SEC affects an older population (60-70 years), while patients with SLT have an average age of 25 years and may exhibit endocrine manifestations. A number of histologic features can be used to distinguish the 2 entities, the most important ones being (1) the presence of areas with the usual pattern of endometrioid carcinoma, and (2) the presence of mucin at the apical borders of the tumor cells. Cytokeratin stains positively, while inhibin and calretinin stain negatively in SEC; the converse is true for SLTs. Based on the clinicopathologic behavior of this entity, SEC should be considered a well-differentiated carcinoma with relatively good prognosis if limited to the ovary.     

Composite small lymphocytic lymphoma and extra-medullary myeloid tumor: a potential diagnostic pitfall

Reported herein is a case of composite small lymphocytic lymphoma (SLL) and extramedullary myeloid tumor (EMT) occurring in the same lymph node. Routine morphologic examination revealed a diffuse proliferation of small mature lymphocytes with numerous irregularly dispersed nodules, closely resembling SLL with prominent proliferation centers or Richter's transformation. Flow cytometric immunophenotyping and immunohistochemical stains demonstrated the presence of SLL cells as well as myeloblasts, confirming the diagnosis of a composite SLL and EMT. Conventional cytogenetics and fluorescence in situ hybridization studies revealed inversion 16 chromosome involving the core binding factor beta and myosin heavy chain 11 genes, characteristic of acute myeloid leukemia with abnormal bone marrow eosinophils and inv(16) or t(16;16) [CBFbeta/MYH11]. In conclusion, the occurrence of SLL and EMT in the same lymph node is rare and multiparameter approach is essential for a definitive diagnosis.     

Unique cell membrane expression of topoisomerase-II alpha as a useful diagnostic marker of liposarcoma

Topoisomerase-II alpha (Topo-II alpha) is known as a cell cycle-related intranuclear marker. To the best of our knowledge, the expression of Topo-II alpha on extranuclear sites has not been reported. The aim of the present study was to determine the usefulness of Topo-II alpha immunostaining for detecting the lipoblasts that are essential to diagnosing liposarcoma. Surgical specimens, including benign lipomatous tumors (four cases), well-differentiated liposarcomas (three cases), myxoid liposarcomas (six cases), pleomorphic liposarcomas (two cases), dedifferentiated liposarcomas (two cases), myxoid malignant fibrous histiocytomas (six cases), and one case of mesenteric panniculitis, were studied. Samples were immunostained using antibodies for Topo-II alpha, S-100 protein and Ki-67. In addition, we used the western blot method to investigate immunohistochemical-affinity in adipocytes. Mature adipocytes and lipoblasts in all of the benign and malignant lipomatous tumors intensively expressed cell contours positivity for Topo-II alpha. Cytoplasm of the lipoblasts occasionally reacted to the antibody and highlighted intracytoplasmic small unilocular, multivacuolated, or bubble-like patterns. Western blot analysis confirmed a 70 kDa product reactive to Topo-II alpha in the cell membrane fragment of mature adipocytes. S-100 protein expressed adipocytes and lipoblasts, but the detection of lipoblasts was not as easy as in Topo-II alpha immunostaining. Immunoreactivity of Ki-67 was limited to the nuclei, and the nuclear labeling index of Ki-67 correlated with that of Topo-II alpha. The immunoreactivity of Topo-II alpha for lipoblasts was more sensitive and obvious than those of S-100 protein. Immunostaining using the antibody for Topo-II alpha seems to be useful in recognizing lipoblasts that have been overlooked in hematoxylin-eosin-stained preparations, and is a useful marker for diagnosing liposarcoma.     

Carcinoembryonic antigen: cell adhesion molecule and useful diagnostic marker

Carcinoembryonic antigen (CEA) was first identified over 30 years ago as a marker of malignant colonic cells, but has since been shown to be expressed by a range of normal epithelial cells. Moreover, CEA is one member of a larger gene family and shares structural homology with other family molecules. Despite this confused picture, CEA is now known to function in several biological roles, including cell-cell adhesion. Its use in the diagnostic setting has also changed over the years, where in routine immunohistochemistry, monoclonal antibodies to CEA are useful in aiding diagnosis when used as part of a panel. Here, recent advances in understanding the biological role(s) that CEA and CEA-related antigens may play in cell adhesion are highlighted, together with results from molecular studies that illustrate how structure can influence the choice of CEA antibodies for use in both the research and diagnostic laboratory.