Application of a 5 Marker Panel to the Routine Diagnosis of Peripheral T-Cell Lymphoma With T-Follicular Helper Phenotype.

The 2017 World Health Organization update introduced a new category of nodal peripheral T-cell lymphoma with T-follicular helper phenotype (PTCL-TFH) defined by expression of at least 2 or 3 TFH markers. Our study assesses the utility of an immunohistochemical panel of 5 TFH markers (CD10, BCL6, PD-1, CXCL13, and ICOS) for identification of TFH phenotype in angioimmunoblastic T-cell lymphoma (AITL) and PTCL not otherwise specified (NOS). Immunohistochemical for the 5 markers was performed on 22 cases of AITL and 29 cases of PTCL-NOS. Cases were reviewed for morphologic features characteristic of AITL. All AITL cases showed expression of ≥2 TFH markers. This panel resulted in reclassification of 41% PTCL-NOS cases to PTCL-TFH. Positive percent agreement for the TFH phenotype is 97% for PD1, 94% for ICOS, 44% for CD10 and CXCL13, and 29% for BCL6. Negative percent agreement for TFH phenotype is 100% for CD10, BCL6, and CXCL13, 82% for ICOS and 71% for PD1. AITL cases were more likely than PTCL-TFH cases to contain expanded CD21-positive follicular dendritic cell meshworks, clear cell cytology and polymorphous inflammatory background; however, there was a significant (P<0.005) Kruskal-Wallis trend in all morphologic variables between the 3 groups suggesting a continuum from PTCL-NOS to PTCL-TFH to AITL. The median number of morphologic features of AITL also correlated significantly with number of TFH markers positive (Spearman coefficient ρ=0.759). In summary, the stain panel chosen will have an impact on cases classified as PTCL-TFH. This entity may exist along a spectrum between PTCL-NOS and AITL.

Immunohistochemical Analysis of Endothelial Cells in Vascular Transformation of Lymph Node Sinuses: Vascular or Lymphatic Differentiation?

INTRODUCTION: Vascular transformation of sinuses (VTS) is an uncommon and benign lesion, defined by conversion of lymph node sinuses into complex, anatomizing and endothelial-lined channels. Despite the name of VTS, which implies a change in differentiation from lymphatic to vascular endothelium, very few studies have systematically examined VTS with modern immunohistochemical markers commonly used in clinical laboratories. It is unclear whether endothelial cells in VTS display pure vascular or lymphatic differentiation, or both. DESIGN: A total of 11 cases with a diagnosis of VTS (identified in the tissue archives of the Cleveland Clinic between 1992 and 2015) were reviewed and confirmed. Twenty cases of benign lymph nodes without specific diagnoses were used as control tissues. Immunohistochemical stains were performed on formalin-fixed, paraffin-embedded lymph node tissue using an automated immunohistochemistry platform with antibodies against CD31, CD34, D2-40, and ERG. Positivity in the VTS lesions was defined as distinct expression in the appropriate cell compartment in ≥20% of cells. In control cases, staining was evaluated in both vascular and lymphatic channels-vascular structures were identified by presence of red cells or well-formed vascular walls and lymphatics by anatomic location and absence of vascular features. RESULTS: In the VTS lesions, D2-40 expression was absent in the lesional endothelial cells of 5/11 (45%) cases. In the cases lacking D240 expression, uninvolved lymphatic endothelium maintained expression. CD34 expression was also seen in 6/11 (54%), CD31 was seen in 10/11 (90%), and ERG expression was seen in all cases. In all the control cases, D240 expression was exclusively seen in lymphatic endothelial cells and not seen in vascular endothelial cells (eg, vascular channels in the hilum). CD34 was weakly positive in the lymphatic endothelium of only 7/20 (35%) control cases, but expressed in 20/20 (100%) control cases in the vascular endothelium. 20/20 (100%) of control cases showed expression of CD31 and ERG in both vascular and lymphatic endothelium. CONCLUSION: VTS lesional endothelial cells demonstrate patterns of vascular markers that show mixed blood vascular and lymphatic features. There appears to be a degree of alignment toward endothelial differentiation with decreased expression of D2-40 in some cases.

Novel MIR143-NOTCH fusions in benign and malignant glomus tumors.

Glomus tumors (GT) have been classified among tumors of perivascular smooth muscle differentiation, together with myopericytoma, myofibroma/tosis, and angioleiomyoma, based on their morphologic overlap. However, no molecular studies have been carried out to date to investigate their genetic phenotype and to confirm their shared pathogenesis. RNA sequencing was performed in three index cases (GT1, malignant GT; GT2, benign GT and M1, multifocal myopericytoma), followed by FusionSeq data analysis, a modular computational tool developed to discover gene fusions from paired-end RNA-seq data. A gene fusion involving MIR143 in band 5q32 was identified in both GTs with either NOTCH2 in 1p13 in GT1 or NOTCH1 in 9q34 in GT2, but none in M1. After being validated by FISH and RT-PCR, these abnormalities were screened on 33 GTs, 6 myopericytomas, 9 myofibroma/toses, 18 angioleiomyomas and in a control group of 5 sino-nasal hemangiopericytomas. Overall NOTCH2 gene rearrangements were identified in 52% of GT, including all malignant cases and one NF1-related GT. No additional cases showed NOTCH1 rearrangement. As NOTCH3 shares similar functions with NOTCH2 in regulating vascular smooth muscle development, the study group was also investigated for abnormalities in this gene by FISH. Indeed, NOTCH3 rearrangements were identified in 9% of GTs, all present in benign soft tissue GT, one case being fused to MIR143. Only 1/18 angioleiomyomas showed NOTCH2 gene rearrangement, while all the myopericytomas and myofibroma/toses were negative. In summary, we describe novel NOTCH1-3 rearrangements in benign and malignant, visceral, and soft tissue GTs.