Metastatic melanoma mimicking solitary fibrous tumor: report of two cases

Dedifferentiated Melanoma: A Diagnostic Histological Pitfall-Review of the Literature with Case Presentation

Dedifferentiated melanoma is a particular form of malignant melanoma with a progressive worsening of the patient's clinical outcome. It is well known that melanoma can assume different histo-morphological patterns, to which specific genetic signatures correspond, sometimes but not always. In this review we address the diagnostic difficulties in correctly recognizing this entity, discuss the major differential diagnoses of interest to the dermatopathologist, and conduct a review of the literature with particular attention and emphasis on the latest molecular discoveries regarding the dedifferentiation/undifferentiation mechanism and more advanced therapeutic approaches.

Dedifferentiated melanomas: Morpho-phenotypic profile, genetic reprogramming and clinical implications

Phenotypic plasticity of malignant melanoma is a well-known phenomenon. Several translational studies and small case series have reported this clinical and biological entity, particularly in metastatic melanoma, showing frequent aberrant expression of non-melanocytic differentiation markers of different lineages, posing remarkable challenges due to several alternative differential diagnoses including undifferentiated carcinoma and sarcomas. When melanoma loses its typical morpho-phenotype by routinely used diagnostic immunohistochemical markers, it is defined as "dedifferentiated melanoma". Historically, this process was closely related to diagnostic interpretative difficulties. In recent years, however, dedifferentiation has been increasingly recognized as an important biological phenomenon that demonstrates the phenotypic and genetic plasticity of melanoma, and specifically the non-irreversibility of the multistep cancerogenesis. Furthermore, dedifferentiation emerged as a general hallmark of cancer evolution and a common denominator of cross-resistance to both targeted and immunotherapy. In this review, we summarize the histopathological features, the genetic and epigenetic bases underlying the dedifferentiated phenotype in melanomas and provide additional support that dedifferentiation is a mechanism of resistance to immunotherapy and targeted therapy.

Multifocal Amelanotic Melanoma of the Hard Palate: A Challenging Case

Among all melanomas, the mucosal type is very rare and may occur in the sino-nasal mucosa, vagina, anus and the oral cavity. At variance with melanomas of the skin, no risk factors, such as familiarity, UV-exposure and skin phenotype, have been clearly identified for such neoplasms. Frequently, the diagnosis is delayed and achieved at advanced stages or when metastases have already occurred. The authors report on a case of mucosal melanoma of the oral cavity presenting as a mass of the hard palate in a 50-year old male, and the corresponding diagnostic-therapeutic pathway.

Immunohistochemical and Molecular Features of Melanomas Exhibiting Intratumor and Intertumor Histomorphologic Heterogeneity

Melanoma is a heterogeneous neoplasm at the histomorphologic, immunophenotypic, and molecular levels. Melanoma with extreme histomorphologic heterogeneity can pose a diagnostic challenge in which the diagnosis may predominantly rely on its immunophenotypic profile. However, tumor survival and response to therapy are linked to tumor genetic heterogeneity rather than tumor morphology. Therefore, understating the molecular characteristics of such melanomas become indispensable. In this study, DNA was extracted from 11 morphologically distinct regions in eight formalin-fixed, paraffin-embedded melanomas. In each region, mutations in 50 cancer-related genes were tested using next-generation sequencing (NGS). A tumor was considered genetically heterogeneous if at least one non-overlapping mutation was identified either between the histologically distinct regions of the same tumor (intratumor heterogeneity) or among the histologically distinct regions of the paired primary and metastatic tumors within the same patient (intertumor heterogeneity). Our results revealed that genetic heterogeneity existed in all tumors as non-overlapping mutations were detected in every tested tumor (n = 5, 100%; intratumor: n = 2, 40%; intertumor: n = 3, 60%). Conversely, overlapping mutations were also detected in all the tested regions (n = 11, 100%). Melanomas exhibiting histomorphologic heterogeneity are often associated with genetic heterogeneity, which might contribute to tumor survival and poor response to therapy.

Detection of driver mutations in BRAF can aid in diagnosis and early treatment of dedifferentiated metastatic melanoma

Dedifferentiated metastatic melanoma can pose a significant diagnostic challenge, especially if the history of primary melanoma is not known or is remote. BRAF and NRAS mutations are common melanoma driver mutations that are usually sequenced to evaluate for treatment targets. We evaluated whether BRAF and NRAS mutational testing could contribute to the diagnosis of dedifferentiated metastatic melanoma when immunostains are negative. Seven patients with melanoma who had an additional diagnosis of poorly differentiated sarcoma with negative melanocytic immunostains were tested for BRAF and NRAS mutations. Three patients showed identical BRAF mutations in the melanoma and the poorly differentiated sarcoma and hence were re-classified as metastatic dedifferentiated melanoma. In these three patients, there was an average delay of 7 months before appropriate testing, workup and treatment for metastatic melanoma was initiated. Two of these patients currently have stable metastatic disease and show sustained therapeutic response to melanoma-specific treatment including BRAF inhibitors. BRAF mutational analysis should therefore be considered in cases of poorly differentiated sarcoma, especially if there is a known history of melanoma or with unusual localization of disease. The administration of melanoma-specific treatments in such dedifferentiated cases can show therapeutic response, highlighting the importance of rendering accurate diagnoses on such cases.

Update on Molecular Pathology of Cutaneous Melanocytic Lesions: What is New in Diagnosis and Molecular Testing for Treatment?

In this article, we give an update on recent findings regarding molecular pathology in cutaneous melanocytic tumors. The focus lies on use of genetics in the diagnosis of distinct subtypes of spitzoid tumors that are often characterized by specific phenotypic–genotypic alterations that can frequently be recognized by adequate histological examination. Typical illustrating cases are given in order to increase recognition of these lesions in daily dermatopathology practice. New molecular findings in the pathogenesis of congenital melanocytic tumors and neurocutaneous melanosis are reviewed. In addition, use of mutation analysis in the differential diagnosis of melanoma metastasis is discussed. Finally, application of mutation analysis in targeted therapy in advanced melanoma with advantages of new techniques such as next generation sequencing is described.