Letters to the Editor
To the Editors:
Since its original description in 1948, the Spitz nevus remains one of the most controversial and diagnostically challenging entities in dermatopathology.1 Its morphological spectrum is wide, and reliable distinction from spitzoid melanoma is often difficult. Recognized histological variants include the pigmented spindle cell (Reed) nevus; the desmoplastic, halo, polypoid, hyalinized, angiomatous, granulomatous, myxomatous, pigmented epithelioid plexiform, tubular, pagetoid, combined, and intraepidermal Spitz nevus.2 Only 1 case of a Spitz nevus showing rosette-like structures has been described, and this pattern is not mentioned in any of the larger published series to date.3 We report a further case showing this unusual morphology with emphasis on distinction from invasive melanoma showing rosette-like structures.
A 6-mm-diameter mole was excised from the lower back of a 29-year-old woman. Histological examination showed a circumscribed and symmetrical compound melanocytic lesion (Fig. 1). The junctional component was predominantly nested and composed of epithelioid melanocytes with spitzoid cytomorphological features, including abundant eosinophilic cytoplasm and vesicular nuclei with eosinophilic central nucleoli. Kamino body formation and junctional cleavage were present. Focal epidermal atrophy and intraepidermal ascent of scattered melanocytes were limited to the center of the lesion. The dermal component was cellular, and the predominant pattern was of epithelioid cells arranged in nests with a peripheral alignment of nuclei and centrally aggregated eosinophilic cytoplasm, resulting in a striking rosette-like appearance (Fig. 2). No central cystic spaces, lumina, or vascular structures were present, and the structures most closely resembled the Homer-Wright rosettes. This florid rosette-like morphology was present throughout the thickness of the lesion, making assessment of maturation with depth difficult (Fig. 3). Rare mitotic activity was present and confined to the upper half of the lesion. No atypical mitoses were observed. There was no expansile growth, nuclear pleomorphism, or hyperchromasia. By immunohistochemistry, there was diffuse S100 and Melan A expression within the melanocytes, and the mib-1 proliferative index was low. HMB-45 expression was confined to the junctional and superficial dermal aspect. A diagnosis of Spitz nevus with Homer-Wright rosette-like structures was rendered.
Rosette-like structures are a rare and poorly documented observation in melanocytic tumors. They occur most frequently in the setting of primary and metastatic melanoma, but their presence in benign melanocytic tumors is exceptional.4–8 Rosette formation has only been demonstrated in a proliferative nodule arising within a congenital nevus, and to our knowledge, there is only 1 previous report of a Spitz nevus showing rosette-like structures presenting on the knee of a 36-year-old white woman.3,9 Most frequently, the rosettes show a peripheral rim of nuclei with a central aggregate of eosinophilic cytoplasm lacking a central lumen or vessel resembling most closely the Homer-Wright rosettes seen in neuroblastoma and peripheral neuroectodermal tumor.3,6–9 The case presented here was remarkable for florid rosette formation affecting almost the entire lesion, including the deep aspect, resulting in a rather monotonous appearance of the dermal component and an impression of impaired maturation with depth. Extensive rosette formation in benign melanocytic lesions may appear alarming and may easily result in an erroneous diagnosis of invasive melanoma. This is of particular importance as distinguishing features may be subtle, as demonstrated recently in a case of a nevoid melanoma with rosette formation.7 Features in favor of a diagnosis of melanoma include the large lesional size and asymmetry, confluence of junctional nests, florid pagetoid spread and consumption of the epidermis, expansile dermal growth, nuclear pleomorphism, and hyperchromasia.
In conclusion, we report only the second case of a Spitz nevus showing a striking rosette-like morphology. Awareness and recognition of this unusual pattern are important to avoid overdiagnosis as melanoma with all its associated implications.
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3. Kantrow S, Kalemeris GC, Prieto V. Spitz nevus with rosette-like structures: a new histologic variant. J Cutan Pathol. 2008;35:510–512.
4. Kacerovska D, Michal M, Sosna B, et al.. Carcinoid-like pattern in melanoma: report of 4 cases. Am J Dermatopathol. 2009;31:542–550.
5. Banerjee SS, Harris M. Morphologic and immunophenotypic variations in malignant melanoma. Histopathology. 2000;36:387–402.
6. Pfohler C, Thirkill CE, Tilgen W. Rosette formation in melanoma: more frequent than suspected? Am J Dermatopathol. 2003;25:360–361.
7. Falconieri G, Luzar B, Angione V, et al.. Primary cutaneous nevoid melanoma with Homer-Wright rosettes: a hitherto unrecognized variant with immunohistochemical and ultrastructural study. Am J Dermatopathol. 2010;32:606–609.
8. Alonso S, Rodríguez-Peralto JL, Ballestín C, et al.. Metastatic malignant melanoma with Homer-Wright rosettes mimicking a neuroblastic tumor. An unusual morphological manifestation. Virchows Arch. 2003;443:108–110.
9. Hoang MP, Rakheja D, Amirkhan RH. Rosette formation within a proliferative nodule of an atypical combined melanocytic nevus in an adult. Am J Dermatopathol. 2003;25:35–39.