Pluripotential Melanoblastoma, a Unifying Concept on Malignancies Arising in Congenital Melanocytic NEVI: Report of Two Cases

Melanoma on congenital melanocytic nevi

Among nevus-associated melanomas, which overall account for 20%-30% of all melanomas, those arising specifically in congenital melanocytic nevi are infrequent, but can be disproportionately frequent in childhood and adolescence. Congenital melanocytic nevi (CMNi) are common benign melanocytic tumors that are present at birth or become apparent in early childhood. They are classified based on the projected adult size. Small and medium-sized CMNi are frequent, whereas large/giant CMNi (over 20 cm in diameter) are rare, but can be associated with high morbidity due to marked aesthetic impairment and the risk of neurocutaneous syndrome or melanoma development. In this setting, melanomas can appear in early childhood and are very aggressive, while the risk of small-medium CMNi of developing melanoma is low and similar to non-congenital melanocytic nevi. Histologically, most melanomas on CMNi initiate their growth at the epidermal-dermal junction, but in large/giant CMNi they can develop entirely in the dermis, in deeper tissues, or in extracutaneous sites (especially in the central nervous system). Most CMNi harbour an NRAS mutation, but other genes are rarely involved, and gene translocations have recently been described. However, no prognostic implications have been associated with the CMN genotype. Melanomas developed on CMNi harbour additional molecular alterations to which the aggressive clinical course of these tumors has been attributed. This review covers the distinctive clinical and pathological aspects of melanomas on CMNi, and includes the epidemiology, etiopathogenesis, clinical and dermoscopic presentation, histological and molecular characteristics, as well as tumour behaviour.

Rhabdomyoblastic Differentiation in Malignant Melanoma in Adults: Report of 2 Cases

Two cases of malignant melanoma are reported in adults exhibiting rhabdomyoblastic differentiation to alert pathologists to this rare variant of malignant melanoma. One of the cases presented as a metastasis in a submandibular lymph node, and the other was a primary skin melanoma. There are only a few published reports on melanocytic tumors with rhabdomyoblastic differentiation, mainly occurring in giant congenital nevi. Both cases reported here were confirmed by immunohistochemistry. Both cases were also studied by electron microscopy, and one showed distinctive ultrastructural features of striated muscle.

Polypoid Dermal Dendrocytic Hamartoma in a Giant Congenital Melanocytic Nevus

Giant congenital melanocytic nevus (CMN) might be complicated by the development of several tumor types, mainly melanoma and rhabdomyosarcoma, but also poorly differentiated neoplasms. Striking polypoid exophytic masses occasionally result from neuroectodermal and neuromesenchymal hamartomatous overgrowths, which lends support to the concept of pluripotential melanoblastomatous and neurocristic origin of these lesions. The present report describes what appears to be a unique example of dermal hamartomatous polypoid CD34+ fibrogenic proliferation devoid of melanin, namely a dendrocytoma, surrounded by the melanocytes from the nevus, located in the skin of the scrotum against a background of giant CMN. The differential diagnosis included dermatofibrosarcoma protuberans, giant-cell fibroblastoma, angiofibroma, Bednar tumor, other types of dermal dendrocytic hamartoma, and neurocristic cutaneous hamartoma. This case lends support to the proposed neurocristic origin of dermal fibrogenic cells.

Rhabdomyoblastic differentiation in metastatic melanoma: making sense of a rare but complex form of mimicry

A case of melanoma with rhabdomyoblastic differentiation is presented in the context of the previously reported cases. The emerging literature seeking to identify the molecular basis of rhabdoid and rhabdomyoblastic differentiation, as well as their poor prognosis, is reviewed. The combination of a diverse range of morphology and the potential for spontaneous primary tumor regression, despite metastasis, makes the accurate diagnosis of melanoma challenging. Histopathology review is often recommended in these cases, as is referral to a specialized cancer center for discussion in a multidisciplinary meeting. Improved recognition of this rare pattern of melanoma morphology may provide the means for omics-based techniques to identify novel therapeutic targets to improve the prognostic outlook for these patients.

Neurogenic tumors of soft tissue

Neurogenic tumors are an uncommon yet important category of soft tissue tumors in children and adolescents because of their frequent association with various genetic syndromes. The heterogeneous cellular composition of the peripheral nerve and the wide metaplastic capacity of the neural crest and its derivatives generate a variety of neoplasms with neurogenic differentiation. This article reviews the clinicopathologic features and differential diagnosis of neurogenic tumors in the first two decades of life, and highlights use of selected ancillary methods for diagnosis.

Malignant neuroectodermal tumor with melanocytic and rhabdomyoblastic differentiation

Malignant melanoma can metastasize widely and vary significantly in its histological appearance; it rarely presents as a deep-seated mass without an obvious primary site elsewhere. Malignant peripheral nerve sheath tumor (MPNST) is a high-grade sarcoma characterized by conventional and epithelioid subtypes. MPNST can demonstrate heterologous differentiation, usually in the form of osteosarcomatous, chondrosarcomatous, or rhabdomyosarcomatous differentiation. MPNST does not harbor true melanocytic differentiation, although epithelioid MPNST typically is diffusely S-100 protein positive and superficially can resemble malignant melanoma. An unusual intra-abdominal mass was recently encountered with features of both melanoma and conventional or epithelioid MPNST containing a fascicular spindle cell component, an epithelioid component with melanocytic differentiation, as well as a rhabdomyosarcomatous component. The terminology “malignant neuroectodermal tumor with melanocytic and rhabdomyoblastic differentiation” is proposed to describe this neoplasm, reflecting the unusual concomittant lines of differentiation as well as offering a possible rationale for nosologically challenging aspects of this neoplasm.

Risk of malignant transformation of congenital melanocytic nevi: a retrospective nationwide study from The Netherlands

PURPOSE

Since the risk of malignant transformation is the most important reason to remove congenital melanocytic nevi, and data vary in the literature, we aimed to determine the incidence of malignant transformation in congenital melanocytic nevi in The Netherlands.

METHODS

The Dutch nationwide pathology database, PALGA (Pathologisch Anatomisch Landelijk Geautomatiseerd Archief), provided anonymous pathology descriptions of all patients registered with congenital melanocytic nevi (giant or nongiant nevus) and of patients with a malignant melanoma within a congenital melanocytic nevus who were diagnosed between January 1, 1989, and December 31, 2000. A comparison was made between cancer incidence in our cohort of patients and the general population by applying the person-year distribution in the cohort to sex-, age- and calendar period-specific reference data obtained from The Netherlands Cancer Registry. Our cohort consisted of 3929 patients.

RESULTS

After a median follow-up time of 4.7 years, a total of 15 cases of malignant melanoma were observed in 19,253 person-years, against 1.23 expected cases. The incidence rate of malignant melanoma was greater than expected on the basis of population rates, overall standardized incidence rate of 12.2 (95 percent confidence interval 9.6 to 15.3). Compared with the general population rates, we observed an increased risk for malignant melanoma, both in men (standardized incidence ratio = 6.4; 95 percent confidence interval 4.1 to 9.6) and women (standardized incidence ratio = 14.1; 95 percent confidence interval 10.5 to 18.7). This is comparable with the higher propensity of women to develop a malignant melanoma. Patients with a giant nevus had a 51.6 percent higher risk of developing a malignant melanoma compared with the general population rates.

CONCLUSION

Our study shows that congenital melanocytic nevi have a significantly higher risk of developing a malignant melanoma compared with the age-, sex-, calendar-period-specific reference data from The Netherlands Cancer Registry.

Adnexal-centered giant congenital melanocyte nevus with extensive ganglioneuromatous component and trisomy 7

Adequate interpretation of clinical and histopathologic features of giant congenital melanocytic nevus (GCMN) in newborns is a continued challenge. A GCMN with three large nodules and three polypoid exophytic tumors presented in the dorsum of a female full-term newborn, the borders exhibiting a spotted grouped pattern. Microscopic examination revealed a peculiar adnexal-centered (eccrine sweat gland ducts, acrosiringia, and hair infundibula) compound nevus expressing pagetoid intraepidermal spreading of epithelioid melanocytes. The nodules represented an extensive ganglioneuromatous component. The neurons and their neuropil were positive for neuron-specific enolase, S-100, synaptophysin, tyrosine hydroxilase, and PGP 9.5. In addition to these components, a poorly differentiated, fusiform, low-mitotic rate population of cells undergoing epithelioid differentiation (and probably neuronal differentiation) with nodular arrangement was also present in the polypoid tumors and deeper parts of the nevus, in part intermixed with the neurons. These cells were vimentin positive but S-100 negative. FISH studies revealed these cells to express three signals for the centromeric probe for chromosome 7 whereas the neuronal component showed just two. Adnexal-centered arrangement of melanocytes has not been emphasized in GCMN. Ganglioneuromatous differentiation has been rarely reported in this condition. Trisomy 7 in GCMN has been reported only once previously.