Mohs excision of melanoma using immunostains can be useful, especially for tumors on the head and neck. For routine excision, margins wider than those currently recommended may be required to ensure tumor clearance. We recommend that (1) biopsies be stained preoperatively for Melan-A and/or HMB-45, (2) a debulking layer be obtained for permanent sections prior to Mohs layers, and positive and negative control specimens from the tumor and distant skin should be employed for comparison of staining patterns. Large-scale prospective studies of in situ and invasive melanoma on the head and neck are necessary.

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Current pathologic criteria cannot reliably distinguish cutaneous anaplastic large cell lymphoma from other CD30-positive T-cell lymphoproliferative disorders (lymphomatoid papulosis, systemic anaplastic large cell lymphoma with skin involvement, and transformed mycosis fungoides). We previously reported IRF4 (interferon regulatory factor-4) translocations in cutaneous anaplastic large cell lymphomas. Here, we investigated the clinical utility of detecting IRF4 translocations in skin biopsies. We performed fluorescence in situ hybridization for IRF4 in 204 biopsies involved by T-cell lymphoproliferative disorders from 182 patients at three institutions. Nine of forty-five (20%) cutaneous anaplastic large cell lymphomas and 1 of 32 (3%) cases of lymphomatoid papulosis with informative results demonstrated an IRF4 translocation. Remaining informative cases were negative for a translocation (7 systemic anaplastic large cell lymphomas; 44 cases of mycosis fungoides/Sézary syndrome (13 transformed); 24 peripheral T-cell lymphomas, not otherwise specified; 12 CD4-positive small/medium-sized pleomorphic T-cell lymphomas; 5 extranodal NK/T-cell lymphomas, nasal type; 4 gamma-delta T-cell lymphomas; and 5 other uncommon T-cell lymphoproliferative disorders). Among all cutaneous T-cell lymphoproliferative disorders, fluorescence in situ hybridization for IRF4 had a specificity and positive predictive value for cutaneous anaplastic large cell lymphoma of 99% and 90%, respectively (p=0.00002, Fisher’s exact test). Among anaplastic large cell lymphomas, lymphomatoid papulosis, and transformed mycosis fungoides, specificity and positive predictive value were 98% and 90%, respectively (p=0.005). Fluorescence in situ hybridization abnormalities other than translocations and IRF4 protein expression were seen in 13% and 65% of cases, respectively, but were non-specific with regard to T-cell lymphoproliferative disorder subtype. Our findings support the clinical utility of fluorescence in situ hybridization for IRF4 in the differential diagnosis of T-cell lymphoproliferative disorders in skin biopsies, with detection of a translocation favoring cutaneous anaplastic large cell lymphoma. Like all fluorescence in situ hybridization studies, IRF4 testing must be interpreted in the context of morphology, phenotype, and clinical features.

PURPOSE More than 80% of patients who undergo sentinel lymph node (SLN) biopsy have no nodal metastasis. Here, we describe a model that combines clinicopathologic and molecular variables to identify patients with thin- and intermediate-thickness melanomas who may forgo the SLN biopsy procedure because of their low risk of nodal metastasis. PATIENTS AND METHODS Genes with functional roles in melanoma metastasis were discovered by analysis of next-generation sequencing data and case-control studies. We then used polymerase chain reaction to quantify gene expression in diagnostic biopsy tissue across a prospectively designed archival cohort of 754 consecutive thin- and intermediate-thickness primary cutaneous melanomas. Outcome of interest was SLN biopsy metastasis within 90 days of melanoma diagnosis. A penalized maximum likelihood estimation algorithm was used to train logistic regression models in a repeated cross-validation scheme to predict the presence of SLN metastasis from molecular, clinical, and histologic variables. RESULTS Expression of genes with roles in epithelial-to-mesenchymal transition (glia-derived nexin, growth differentiation factor 15, integrin-β3, interleukin 8, lysyl oxidase homolog 4, transforming growth factor-β receptor type 1, and tissue-type plasminogen activator) and melanosome function (melanoma antigen recognized by T cells 1) were associated with SLN metastasis. The predictive ability of a model that only considered clinicopathologic or gene expression variables was outperformed by a model that included molecular variables in combination with the clinicopathologic predictors Breslow thickness and patient age (area under the receiver operating characteristic curve, 0.82; 95% CI, 0.78 to 0.86; SLN biopsy reduction rate, 42%; negative predictive value, 96%). CONCLUSION A combined model that included clinicopathologic and gene expression variables improved the identification of patients with melanoma who may forgo the SLN biopsy procedure because of their low risk of nodal metastasis.

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