Malignant melanoma with metaplastic cartilaginous transdifferentiation: A case report

Cartilaginous Transdifferentiation in Melanoma: A Diagnostic Challenge

Malignant melanoma is a formidable tumor originating from melanocytes of neural crest origin, found in various anatomical locations, primarily in the skin, followed by the eyes and mucosal membranes. This tumor stands out due to its remarkable phenotypic diversity. Transdifferentiation, the process of differentiation into cell lineages other than the one from which the tumor originated, and phenotypic plasticity, characterized by changes in behavior, morphology, and physiology in response to different environmental conditions, can make melanoma a diagnostic conundrum for unwary pathologists. In this case report, we present a challenging case of melanoma with cartilaginous transdifferentiation to shed light on its clinical, pathological, and molecular aspects.

Subungual melanoma with cartilaginous differentiation: Molecular insights

Melanoma's rare capacity to undergo heterologous differentiation can create significant diagnostic challenges. The molecular mechanisms underlying this phenomenon are not well understood. We present an unusual case of subungual melanoma exhibiting extensive cartilaginous differentiation and provide insights into its molecular and cytogenomic features. Histopathologically, the tumor was predominantly composed of nodules of malignant cartilage in association with a smaller population of nested epithelioid to rhabdoid cells. Immunohistochemically, the tumor cells in both components were positive for S100, SOX10, and PRAME, and were negative for Melan-A and HMB-45. Molecular analysis by whole exome DNA sequence did not detect any pathogenic variants in genes commonly implicated in melanoma. Additional analysis by SNP chromosomal microarray revealed a complex genome characterized by numerous chromosomal losses and gains, including a homozygous deletion of the CDKN2A locus and a heterozygous deletion of the locus containing EXT2, a tumor suppressor implicated in hereditary multiple osteochondromas and secondary chondrosarcomas. This case underscores the importance of recognizing cartilaginous differentiation as a rare manifestation of melanoma, particularly at subungual sites, and suggests that at least some of these melanomas may be driven by non-canonical molecular pathways.

Metastatic Nodular Melanoma with Angiosarcomatous Transdifferentiation-A Case Report and Review of the Literature

Diagnosing cutaneous melanomas relies mainly on histopathological analysis, which, in selected cases, can be aided by immunohistochemical evaluation of conventional melanocytic markers. Nevertheless, these malignancies, particularly in metastatic settings, may display divergent differentiation with unusual histological and immunohistochemical features. In this context, we present the case of a 65-year-old male diagnosed with typical superficial spreading melanoma who developed recurrence and metastatic lesions featuring angiosarcomatous differentiation. The diagnosis of the initial tumour and the subsequently dedifferentiated lesions was confirmed by ample immunohistochemical analysis, which included several melanocytic markers, as well as mesenchymal and vascular markers. The recurrent tumour and lymph nodes metastases were completely negative for Melan-A and PRAME, and focally positive for SOX10. Additionally, they also displayed diffuse, intense positivity for CD10 and WT1 and focal positivity for CD99, ERB, and CD31. Thus, the diagnosis of primary cutaneous melanoma with recurrent and metastatic divergent angiosarcomatous differentiation was established. This occurrence is particularly rare and can pose important diagnostic challenges. Therefore, in addition to presenting this highly unusual case, we also performed a comprehensive review of the literature on divergent differentiation in melanomas.

Primary Undifferentiated/Dedifferentiated Cutaneous Melanomas-A Review on Histological, Immunohistochemical, and Molecular Features with Emphasis on Prognosis and Treatment

Diagnosing cutaneous melanoma is usually straightforward based on these malignancies' histopathological and immunohistochemical features. Nevertheless, melanomas can imitate various other neoplasms, sometimes lacking the expression of conventional melanocytic markers and expressing non-melanocytic ones. Furthermore, divergent differentiation is more often encountered in metastatic melanomas and is still poorly described in primary cutaneous melanomas, and little is known about these patients' prognosis and therapeutic approach. Therefore, we reviewed the literature on undifferentiated/dedifferentiated cutaneous melanomas, and we discuss the histological, immunohistochemical, and molecular profiles of undifferentiated/dedifferentiated cutaneous melanomas to understand these peculiar lesions better and improve their diagnostic algorithm. In addition to this, we also discuss how different genetic mutations may influence prognosis and become potential therapeutic targets.

Gross, histologic, and immunohistochemical characteristics of cutaneous chromatophoromas in captive bearded dragons

Chromatophoromas are neoplasms that develop from the dermal pigment-bearing and light-reflecting cells (chromatophores) in the skin of reptiles, fish, and amphibians. Seventeen cutaneous chromatophoromas were identified from 851 bearded dragon submissions (2%) to a private diagnostic laboratory in a 15-y period. No sex predilection was found. Ages ranged from 9 mo to 11 y. Chromatophoromas most commonly were single, raised, variably pigmented masses or pigmented scales on the trunk, and less commonly the extremities or head. Microscopically, iridophoromas, melanophoromas, mixed chromatophoromas, and nonpigmented chromatophoromas were identified. Neoplasms were often ulcerated and invaded deep into the subcutis and muscle. Most commonly, nuclear atypia was mild-to-moderate, and mitotic count was low. Six neoplasms had abundant, periodic acid-Schiff-positive, mucinous stroma. Histologic examination was often adequate to diagnose chromatophoromas in bearded dragons given that 11 of 17 had some degree of pigmentation, although it was often scant. IHC for S100 and PNL2 could be helpful to diagnose poorly pigmented neoplasms. No lymphatic invasion or metastases at the time of excision were noted in any of the cases. Follow-up data were available for 6 cases, with no reports of recurrence or neoplasia-related death. Two cases had elevated mitotic counts and nuclear pleomorphism, which has been associated with metastasis in other reports of bearded dragon chromatophoromas. In general, it appears that aggressive surgical excision is often curative, but monitoring may be warranted for cases in which tumors had high mitotic count and nuclear pleomorphism.

A rare case of invasive melanoma likely arising from passenger melanocytes of a basal cell carcinoma

Neoplasms consisting of different cell lineages within a single skin specimen are rare, yet well documented in the literature. However, to date, there appears to be no report of invasive melanoma arising directly from the passenger melanocytes of a basal cell carcinoma (BCC). We present a case of a 91-year-old male with a suspicious lesion on the ear. Histopathology and immunohistochemical staining revealed BCC closely intertwined with invasive melanoma that exhibited foci of chondroid differentiation. The melanoma appeared to arise from the benign-appearing passenger melanocytes of the BCC and lacked connection to the overlying epidermis or an in situ component. Multiple dermatopathologists reviewed the case and agreed that the most likely explanation for the histopathologic findings was that the invasive melanoma arose from the passenger melanocytes within the BCC.

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.