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Objectives: Detection of BRAF V600E mutations in hairy cell leukemia (HCL) has important diagnostic utility. In this study, we sought to compare immunohistochemistry with an antibody specific for this mutation to a sensitive molecular assay., Methods: The performance of the BRAF V600E-specific VE1 antibody was compared with that of allele-specific polymerase chain reaction (PCR) in 22 formalin-fixed, paraffin-embedded (FFPE) specimens with HCL involvement, along with nine splenic marginal zone lymphomas (SMZLs), 10 follicular lymphomas (FLs), 10 mantle cell lymphomas (MCLs), and 10 chronic lymphocytic leukemia/small lymphocytic lymphomas (CLL/SLLs). An additional 11 SMZLs, 100 FLs, 20 MCLs, 83 CLL/SLL specimens, and 49 reactive tonsils within tissue microarrays were stained with VE1., Results: A BRAF V600E mutation was detected in 17 (77.3%) of 22 HCL cases by PCR. Immunohistochemistry demonstrated VE1 staining in 20 (90.9%) cases, identifying low-level (~1%) involvement in three HCL cases that were mutation negative by PCR. Evaluation of additional material from these patients confirmed the presence of BRAF V600E. Thirty-nine non-HCL cases were negative by both methods. Within tissue microarrays, weak false-positive staining was observed in two (0.8%) of 263 non-HCL cases., Conclusions: VE1 immunohistochemistry is more sensitive than allele-specific PCR in FFPE bone marrow specimens and can be applied to decalcified core biopsy specimens that are not appropriate for molecular techniques., (Copyright© by the American Society for Clinical Pathology.)

* Context.--Sinonasal papillomas and carcinomas are uncommon head and neck neoplasms that comprise a broad clinicopathologic and morphologic spectrum, and thus frequently represent a diagnostic challenge for surgical pathologists. Recent molecular interrogation of these tumors has delineated a number of recurrent alterations that correspond to distinct entities with potential diagnostic and/or therapeutic clinical utility. Objective.--To summarize the salient clinicopathologic, morphologic, and molecular features of sinonasal papillomas and carcinomas. Data Sources.--Review of pertinent literature regarding sinonasal papillomas and sinonasal carcinomas. Conclusions.--Despite their relative rarity in many surgical pathology practices, sinonasal papillomas and carcinomas frequently demonstrate characteristic morphologic features that are important for accurate diagnosis. Given our emerging understanding of the molecular basis for these tumors, judicious use of available ancillary tools--including immunohistochemistry and in situ hybridization--may be helpful in subsets of cases, whereas additional molecular testing may be useful for diagnostically challenging and/or clinically aggressive sinonasal tumors. (Arch Pathol Lab Med. 2019;143:1304-1316; doi: 10.5858/arpa.2019-0372-RA), Sinonasal papillomas and carcinomas are uncommon head and neck tumors that constitute a number of biologically distinct neoplasms. Some of these tumors are associated with specific environmental exposures (ie, tobacco, [...]

Primary cutaneous T‐cell lymphoma (CTCL) comprises a heterogeneous group of neoplasms with variable clinical behavior. Immunophenotypic switch (IS) is a phenomenon that occurs during lymphoma progression and is defined by an alteration in the immunophenotypic expression of a tumor with retention of its genotypic signature. This has been well‐recognized in hematopoietic neoplasms; however, it has been rarely reported in CTCL and its clinical implications are not well understood. We present the clinical, histopathologic, immunophenotypic, and genetic findings of three cases of CTCL that demonstrated IS post treatment with variable outcomes. We add our cases to the small number previously reported to increase awareness of this phenomenon and its diagnostic challenge. [ABSTRACT FROM AUTHOR]

Cutaneous syncytial myoepithelioma is a recently described rare tumor of the dermis. It is derived and composed purely of myoepithelial cells and shows a characteristic syncytial growth pattern of neoplastic cells with little intervening stroma and no recognizable ductal structures. It represents a diagnostic challenge to dermatopathologists given its rarity and unusual immunophenotype. Molecular testing for rearrangement of the EWSR1 gene plays a significant role in confirming the diagnosis in most cases. Herein, we present 2 cases with mundane clinical presentations and challenging histopathological findings. In both cases, the lesion was composed of relatively well-circumscribed proliferation of epithelioid and spindle cells in the superficial dermis growing in a syncytial fashion and showing focal adipocytic metaplasia. The 2 cases had slightly different immunohistochemical profiles, but shared focal positivity for S100, EMA and pan-keratin or p63. Break-apart FISH demonstrated the presence of an EWSR1 gene rearrangement confirming the diagnosis in both cases. We discuss the most important differential diagnoses, particularly melanocytic lesions and epithelioid sarcoma and the original diagnostic considerations that the cases were referred to us with. We also review the molecular features and spectrum of immunohistochemical findings in these lesions and their role in excluding entities in the differential diagnosis. [ABSTRACT FROM AUTHOR]