Hyalinizing spindle and epithelioid cell nevus. A study of five cases of a distinctive histologic variant of Spitz's nevus

The Spectrum of Spitz Melanocytic Lesions: From Morphologic Diagnosis to Molecular Classification

Spitz tumors represent a distinct subtype of melanocytic lesions with characteristic histopathologic features, some of which are overlapping with melanoma. More common in the pediatric and younger population, they can be clinically suspected by recognizing specific patterns on dermatoscopic examination, and several subtypes have been described. We now classify these lesions into benign Spitz nevi, intermediate lesions identified as “atypical Spitz tumors” (or Spitz melanocytoma) and malignant Spitz melanoma. More recently a large body of work has uncovered the molecular underpinning of Spitz tumors, including mutations in the HRAS gene and several gene fusions involving several protein kinases. Here we present an overarching view of our current knowledge and understanding of Spitz tumors, detailing clinical, histopathological and molecular features characteristic of these lesions.

Chondroid atypical spitzoid melanocytic tumor

Chondroid stromal change is very rare in melanocytic nevi. We present a severely atypical symmetrical Spitz tumor on the right arm of a 24-years-old man. It showed maturation and occasional mitotic figures. The melanocytes were intermingled with cartilaginous stroma. The Ki67 proliferative rate was 5%. It was weakly positive for p16 and negative for BRAF/V600E. BAP1 expression was preserved. PCR for Myriad myPath^® Melanoma test was also negative.

Spitz Tumors of the Skin

Spitz tumors are melanocytic neoplasms hallmarked by large cell size, lack of high-grade atypia, and a regular architecture. Most are nonpigmented or poorly pigmented. Malignant potential ranges from absent (Spitz nevus), to fully present (spitzoid melanoma), with a further, ill-defined group of Spitz tumors with limited metastatic potential. Microscopic evaluation may prove inconclusive in some instances, resulting in a verdict of Spitz tumor of uncertain malignant potential (STUMP). STUMP is, therefore, not an entity, and should not be equated with Spitz tumors with limited metastatic potential. Novel diagnostic techniques are yielding promising results, and further evaluation is ongoing.

Spitz nevus: a clinicopathological study of 349 cases

Spitz nevus is an infrequent, usually acquired melanocytic nevus composed of epithelioid and/or spindle melanocytes that can occasionally be confused with melanoma. Currently, there are no immunohistochemical markers or molecular biology techniques that can be used to make an entirely safe diagnosis of Spitz nevus or melanoma in problematic cases. A retrospective study has been carried out that included all the cases diagnosed as Spitz nevus from our files. Follow-up information of the patients was unavailable. Three hundred forty-nine cases of unequivocal Spitz nevi were included, and their clinical and histopathological parameters were reviewed. One hundred and forty patients (40%) were 15 years old or younger, with a male to female ratio of 1:1. In patients older than 15 years, there was an evident predominance of women, with a male to female ratio of around 1:3. Spitz nevus was most commonly located on the lower extremities, followed by the trunk in both children and adults. Despite the fact that the head and neck were the third most common location in children, it was a much more frequent location in children than in adults. The constitution by epithelioid and/or spindled cells was the only histopathological finding present in 100% of cases. The other pathological findings studied were, from more to less frequent: maturation (72%), inflammatory infiltrate (70%), epidermal hyperplasia (66%), melanin (50%), telangiectasias (40%), Kamino bodies (34%), desmoplastic stroma (26%), mitosis (23%), pagetoid extension (13%), and hyalinization of the stroma (8%). Hyalinization was the only histopathological parameter that was statistically more frequent in adults than in children.

The small leucine-rich proteoglycan lumican inhibits melanoma progression

Lumican is a member of the small leucine-rich proteoglycan (SLRP) family. It contributes to the organisation of the collagen network and plays an important role in cell migration and tissue repair. The present study aimed to determine the influence of lumican expression on adhesion, anchorage-dependent and -independent growth, migration, in vitro invasion and in vivo melanoma growth. For that purpose, B16F1 mouse melanoma cells were stably transfected with an expression plasmid containing the complete lumican cDNA. Lumican expression by tumor cells did not change the proliferative activity of mouse melanoma cells in monolayer culture and did not influence either cell adhesion to extracellular matrix gel or type I collagen or cell spreading on these substrates. In contrast, lumican-transfected cells were characterized by a strong reduction of their anchorage-independent proliferation in agarose gel and capacity to invade extracellular matrix gel. After subcutaneous injections of transfected B16F1 cells in syngenic mice, lumican expression significantly decreased subcutaneous tumor formation in vivo, with a concomitant decrease of cyclin D1 expression. Lumican induced and/or increased the apoptosis of B16F1 cells. The results suggest that lumican is involved in the control of melanoma growth and invasion and may be considered, like decorin, as an anti-tumor factor from the extracellular matrix.

Hyalinizing Spitz Nevus: Spindle and Epithelioid Cell Nevus with Paucicellular Collagenous Stroma

Hyalinizing spindle and epithelioid cell nevus (Spitz nevus) is an uncommon melanocytic lesion. The histologic features of this benign tumor can mimic those of certain benign (dermatofibroma and desmoplastic cellular blue nevus) and malignant (metastatic carcinoma and malignant melanoma) neoplasms. We report a woman with a hyalinizing Spitz nevus and review the clinical characteristics, histologic features, and differential diagnosis of this lesion. The lesion presented as an asymptomatic red firm nodule on her abdomen. Microscopic examination showed a symmetric lesion in the dermis. The neoplastic cells were large and epithelioid-shaped or plump and spindle-shaped. They were present as isolated individual cells, single cells in a linear pattern, small nests, and fascicles in a paucicellular hyalinized stroma. Neoplastic cells with prominent eosinophilic nucleoli were evenly exhibited from the superficial to deep lesion. Diffuse expression of S-100 protein and absence of staining with antibodies to cytokeratin and HMB-45 were observed. The features were diagnostic of a hyalinizing Spitz nevus. Hyalinizing Spitz nevus is a benign lesion whose histologic features may mimic dermatofibroma, desmoplastic cellular blue nevus, metastatic carcinoma, and malignant melanoma. Immunohistochemical studies are helpful to differentiate these lesions.

Myxoid Spitz nevus

BACKGROUND

The deposition of extracellular mucin has not been described in Spitz nevus and herein such a case is reported.

METHODS

A 6-year-old male presented with a growing 1.0-cm pigmented lesion on his left anterior knee. The lesion was excised.

RESULTS

The histologic sections demonstrated a symmetrical and dome-shaped proliferation of spindle and epithelioid melanocytes with sharp lateral demarcation at the dermal-epidermal junction and within the superficial dermis. Features of Spitz nevus such as retraction from the epidermis, eosinophilic bodies, and uniform cytologic atypia were seen. Of interest, there was marked mucin deposition within the epidermal clefts and between the neoplastic cells. The mucin was highlighted by alcian blue and colloidal iron stains, and it was negative with mucicarmine and periodic acid-Schiff stains.

CONCLUSION

Awareness that soitz nevi can rarely have extracellular mucin helps in avoiding diagnostic pitfalls.

Spitz nevus and its histologic simulators

Spitz nevi continue to pose a considerable diagnostic challenge to the histopathologist. Key features of Spitz nevus and its variants are discussed and contrasted with the telltale signs of malignancy of "Spitzoid" melanomas. The importance of the histologic features of the deep, rather than superficial, part of the lesions is emphasized.

Angiomatoid Spitz nevus: a distinct variant of desmoplastic Spitz nevus with prominent vasculature

Five cases of a distinctive variant of desmoplastic Spitz nevus are reported. To the best of our knowledge, this tumor has never been described previously. Clinically, it presents itself as a solitary papule on the extremities of young adults. Microscopically, it shows predominance of solitary melanocytes with epithelioid appearance over cell nests. They are embedded in a prominent fibrous stroma with many densely arranged, small blood vessels with plump endothelia not seen in other Spitz nevi. Because of its resemblance to a vascular tumor, the name angiomatoid Spitz nevus is proposed for this lesion. Absence of recurrences or metastases after complete excision in all cases supports the benign nature of the tumor.

Hyalinizing Spitz nevus

A seventeen-year-old Korean girl had a reddish-brown papular lesion on the nose. Histopathologically, it proved to be a "hyalinizing Spitz nevus" with the characteristic features of a discohesive growth pattern of nevus cells and hyalinized stroma. Immunohistochemical stains showed positive reactivity of nevus cells with S-100 protein and Vimentin and negative stainings with HMB45, CD68, CEA and low molecular weight cytokeratin. Hyalinizing Spitz nevus may represent a variant in the spectrum of Spitz nevus.

Recent developments in the pathology of melanocytic neoplasia

This article selectively discusses clinically relevant aspects of the pathology of cutaneous melanocytic neoplasms, from the literature of the past recent years. Topics include the changing role of immunohistochemistry in diagnosis, the controversies over dysplastic nevi, description of other specialized variants of melanocytic nevi, diagnosis of melanocytic neoplasms of acral skin, and melanoma occurring in childhood. Several variants of melanoma including desmoplastic and spindle-cell types, verrucous melanoma, epidermotropic melanoma, and melanoma of the female genitalia are reviewed. The issue of appropriate margins of resection for melanoma and the use of Mohs Micrographic surgery for this tumor are considered. Finally, a review of the sentinel node biopsy technique and of nodal nevi is presented.

Desmoplastic malignant melanoma on the buttock of an 18-year-old girl: differentiation from desmoplastic nevus

Melanocytic proliferation in young people may sometimes pose a diagnostic dilemma. This is particularly so when a desmoplastic component is present. Because the two main differential diagnoses, desmoplastic malignant melanoma and desmoplastic Spitz nevus, share some morphologic features, the diagnosis of desmoplastic malignant melanoma may be overlooked. Distinction between the two is important because they show completely different biological behavior. The age of patient, site of lesion, histologic findings of melanocytic atypia, neurotropism, mitosis, and maturation help to distinguish the two entities. We report a case of desmoplastic malignant melanoma occurring in the buttock of an 18-year-old Chinese girl. Histologically, it had typical features of desmoplastic malignant melanoma with junctional melanocytic atypia and prominent neurotropism. Clinical and histologic differences between desmoplastic malignant melanoma and desmoplastic Spitz nevus are reviewed. We conclude that although desmoplastic Spitz nevus occurs much more commonly in adolescents, desmoplastic malignant melanoma can occur in this age group and even in non-sunexposed skin. Microscopic findings remain the mainstay that guides the final diagnosis.

The melanocyte differentiation pathway in spitz nevi

The nature of Spitz nevi is poorly understood, and their distinction from malignant melanoma can be difficult. Although there is general agreement on the diagnostic criteria, experts continue to have some differences, and controversial cases are not rare. A major obstacle to progress in this area is the lack of basic knowledge about melanocyte differentiation in Spitz nevi, as compared with ordinary nevi and malignant melanomas. Based on the hypothesis that normal melanocytes may have a differentiation pathway with discrete stages, it is suggested that the features of Spitz nevi may reflect homeostatic mechanisms governing maturation in the melanocyte differentiation pathway, whereas those of malignant melanomas may reflect carcinogen-induced aberrations. This perspective may be helpful in the continuing effort to develop optimal criteria for the differential diagnosis of Spitz nevi from malignant melanomas.

Desmoplastic melanoma of the vulva

The clinical and pathological features of a nonulcerated desmoplastic melanoma in the vulva of a 52-year-old woman are presented. Pleomorphic neoplastic spindle cells, fibroblasts and collagen formed a poorly demarcated 18 mm dermal mass. No adjacent intraepidermal component was seen. Immunoreactivity was demonstrated for S100 protein, vimentin, neuron-specific enolase and actin, but not for HMB-45, CAM 5.2, cytokeratin, epithelial membrane antigen, desmin or CD34. Electron microscopic examination was noncontributory. Treatment included a left hemivulvectomy with ipsilateral groin node dissection followed by radiotherapy. The tumor recurred six weeks later and was unresectable. The patient is alive with symptoms nine months after presentation. This is the first case report of a vulvar desmoplastic melanoma without neural involvement or an intraepidermal component. The variable tumor cytomorphology, nonspecific immunohistochemical and ultrastructural features render a diagnosis more difficult than with other primary cutaneous melanomas.