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Melanocytic lesions have a wide morphological spectrum, ranging from benign nevi to malignant melanoma. In contrast to a diagnosis of a benign nevus, a diagnosis of melanoma could mean intensive treatment, lifetime monitoring, and a worse prognosis. Therefore, melanocytic tumors are notoriously challenging and associated with a high risk of litigation in surgical pathology. After describing the basic features of nevi and melanoma, this article describes the detailed clinical and histological features of those lesions that share many similar features with melanoma. The entities included are Spitz nevi and atypical Spitz tumors (AST), Reed nevus, dysplastic nevus, cellular blue nevus (CBN), deep penetrating nevus, combined nevus, recurrent nevus, irritated nevus, congenital pattern nevus, acral nevus, and nevi of special sites. Knowledge of these imitators can help pathologists distinguish between benign and malignant cases and avoid misdiagnosis.

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Spitz nevus (SN) is a benign melanocytic lesion with cytologic and architectural atypia. It is sometimes difficult to distinguish SNs from atypical Spitz tumor (AST), Spitz melanoma, or conventional melanoma. SNs frequently develop in Caucasians and appear on the skin of the head and lower extremities. Lesions on the ear in Asian populations are rare. Here, we report a "red Spitz tumor" on the ear of a Chinese 18-year-old boy. Dermoscopic examination revealed possibly malignant features presented as polymorphous vessels along with central white area, pseudo-network depigmentation and atypical peripheral globular pattern. The results of histopathological examination strongly suggested that the neoplasm was a compound SN and no recurrences or metastases occurred during 1-year follow-up post-surgery. Further, we review the literature on 4 previously reported cases of SN on the ear and summarize the main points of SN diagnosis and differential diagnosis with atypical Spitz tumors and melanoma.

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BACKGROUND/OBJECTIVES: The diagnostic distinction between atypical Spitz tumor (AST) and malignant melanoma (MM) in pediatric tumors is challenging. Molecular tests are increasingly used to characterize these neoplasms; however, limited studies are available in pediatric patients. This study aimed to provide a genomic comparison of pediatric MM and AST in the context of comprehensive clinical annotation. METHODS: Pediatric patients diagnosed with MM (n=11) and AST (n=12) were compared to a cohort of 693 adult melanoma patients. DNA next-generation sequencing assessed kinase gene fusions, tumor mutational burden, sequence variants, copy number alterations, structural variants, microsatellite instability, and mutational signatures. RESULTS: Seven AST cases and eight MM cases were successfully sequenced. Kinase gene fusions were identified in both the MM and AST cohorts (NTRK1, ROS1, and MET). MM cases had TERT, BRAF, and CDKN2A alterations, which were not identified in the AST cohort. Tumor mutational burden (TMB) analysis showed pediatric ASTs had an average of 2.82 mutations/Mb, pediatric MM had an average of 5.7 mutations/Mb, and adult MM cases averaged 18.8 mut/Mb. One pediatric MM case had an elevated TMB of 15 mutations/Mb and a UV mutational signature. CONCLUSIONS: These data expand our understanding of pediatric malignant melanoma. The differences between the molecular signatures for AST and MM are not statistically significant, and histopathology remains the gold standard for the diagnosis of pediatric AST and MM at this time. With more data, molecular studies may provide additional support for diagnosis and targeted therapeutics.

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The recent WHO classification of skin tumors has underscored the importance of acknowledging intermediate grade melanocytic proliferations. A multistep acquisition of oncogenic events drives the progressive transformation of nevi into melanomas. The various pathways described are modulated by the initial oncogenic drivers that define the common, blue, and Spitz nevi groups. Intermediate lesions are most often the result of a clonal evolution within such nevi. Based on this established classification, we have suggested for each pathway a practical diagnostic approach, benefiting from the recently developed molecular tools, both in the setting of general pathology labs and expert centers. Moreover, recommendations regarding the re-excision and clinical follow-up are given to support decision-making in multidisciplinary tumor boards.

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BACKGROUND: Spitz nevi (or tumors) are noncancerous growths that are found particularly in the pediatric population. Their histologic features overlap with melanoma, but they have a favorable prognosis, even when showing atypical features. OBJECTIVES: The aim of this research is to examine whether Spitz nevi can be sufficiently removed by adequate shave excisions without a subsequent excision. METHODS: Melan-A stained shave removal specimens (SRS) were obtained for 58 consecutively diagnosed Spitz nevi, along with slides of their postshave excision specimens. The SRS were reviewed for negative (clear) margins, defined as no neoplastic melanocytes detected within <0.2 mm of the deep and lateral margins of the specimen. Postshave excision specimens were reviewed for residual or recurrent lesions. RESULTS: The 15 shave excision specimens with negative margins had no corresponding residual lesions on postshave specimens. There were no recurrences in any of the cases in an average of 17 months of follow-up. CONCLUSIONS: Observation may be a logical approach for the management of Spitz nevi when shave removal achieves clear margins and the lesion lacks atypical features.

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BACKGROUND: Spitzoid neoplasms may pose significant diagnostic problems because in a fraction of them it is quite difficult or impossible to establish if they are benign or malignant lesions. An extraordinarily large number of studies have been made in attempts to solve this problem; regrettably, the histological criteria proposed and the various special sophisticated techniques employed have proven to be ineffective in making this distinction with confidence. OBJECTIVES: To explore the possible causes for this diagnostic failure and an attempt to identify the source of this problem. METHOD: A historical and technical analysis of the specialized literature is performed, critically evaluating the main points of this controversial topic. RESULTS: The reasons for the diagnostic failure in Spitzoid neoplasms are not clear but could be the result of inappropriate conceptual representation. The analysis of available data and a rational review of old and new assumptions and concepts may suggest a different representation for Spitzoid neoplasms: Spitz nevus, atypical Spitz tumor and Spitzoid melanoma, rather than being three different tumors that are difficult or impossible to distinguish with assurance, could be viewed as one unique entity, Spitz tumor (ST). This tumor is a low-grade malignant neoplasm, in which the amount of intrinsic risk is variable, ranging from very low to high (ST1, ST2, ST3), and malignant potential could be estimated. CONCLUSIONS: The proposed alternative representation of Spitzoid neoplasms as a unique tumor may help in overcoming the difficulty in diagnosis of these tumors.