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Pigmented epithelioid melanocytoma (PEM) is a subtype of melanocytic tumor with frequent involvement of the sentinel lymph node but rare distant metastasis. Rendering a diagnosis and prognosis based on histology can be challenging. Recent genomic studies identified 2 molecular variants of PEM. One variant is characterized by the activation of the mitogen-activated protein kinase pathway and inactivation of the PRKAR1a gene. The other is associated with genomic fusions involving the protein kinase C ( PRKC ) gene family.We investigated the molecular and clinicopathologic features of previously unreported PEM cases to improve tumor classification and report new classes of PEM.Next-generation sequencing and histomorphologic assessment was performed on 13 PEM cases.We identified 2 novel PEM classes. Three cases harbored PRKAR1a inactivation and genomic fusions ( ALK , NTRK , and MAP3K8 ). These tumors had overlapping histologic features with pigmented Spitz neoplasms. Three cases had genomic fusions involving PRKCB . These cases had overlapping features with PRKCA fusions but, in 2 cases, had a notable spindle cell component.The overall sample size and amount of clinical follow-up is limited, leaving some uncertainty regarding the expected clinical course of these novel cases.PRKAR1a-inactivated/Spitz fusion-associated PEMs and PRKCB fusion-associated PEMs represent 2 new molecular classes of PEM.

Atypical Spitzoid melanocytic tumors are diagnostically challenging. Many studies have suggested various genomic markers to improve classification and prognostication. We aimed to assess whether next-generation sequencing studies using the Tempus xO assay assessing mutations in 1711 cancer-related genes and performing whole transcriptome mRNA sequencing for structural alterations could improve diagnostic agreement and accuracy in assessing neoplasms with Spitzoid histologic features. Twenty expert pathologists were asked to review 70 consultation level cases with Spitzoid features, once with limited clinical information and again with additional genomic information. There was an improvement in overall agreement with additional genomic information. Most significantly, there was increase in agreement of the diagnosis of conventional melanoma from moderate (κ=0.470, SE=0.0105) to substantial (κ=0.645, SE=0.0143) as measured by an average Cohen κ. Clinical follow-up was available in all 70 cases which substantiated that the improved agreement was clinically significant. Among 3 patients with distant metastatic disease, there was a highly significant increase in diagnostic recognition of the cases as conventional melanoma with genomics (P

Spitzoid melanocytic neoplasms can be challenging to diagnose on histopathology alone. Next-generation sequencing (NGS) offers promise as a valuable aid in the diagnosis. Recently, one study reported increased inter-rater agreement in the diagnosis of spitzoid melanocytic neoplasms among 20 expert melanoma pathologists after incorporating NGS data. We hypothesized that NGS would carry a similar utility in a broader group of dermatopathologists and general pathologists.Sixty-three participants of a live online (www.Dermpedia.org) CME course rendered a diagnosis on 70 cases composed of melanocytic neoplasms with spitzoid features. In Survey 1, cases included HE slides and demographic information only, while Survey 2 included NGS data.With NGS information, inter-rater agreement significantly improved from "fair" to "almost perfect" and from "fair" to "substantial" for categorizing lesions as Spitz versus non-Spitz and conventional melanoma versus not, respectively. There was also an increase in diagnostic accuracy, evidenced by improved recognition of three metastatic tumors as being conventional melanomas.The study supports the adoption of NGS as a valuable diagnostic adjunct for both expert and broader dermatopathologists in their assessments of spitzoid neoplasms.

ImportanceA standardized pathology classification system for melanocytic lesions is needed to aid both pathologists and clinicians in cataloging currently existing diverse terminologies and in the diagnosis and treatment of patients. The Melanocytic Pathology Assessment Tool and Hierarchy for Diagnosis (MPATH-Dx) has been developed for this purpose.ObjectiveTo revise the MPATH-Dx version 1.0 classification tool, using feedback from dermatopathologists participating in the National Institutes of Health–funded Reducing Errors in Melanocytic Interpretations (REMI) Study and from members of the International Melanoma Pathology Study Group (IMPSG).Evidence ReviewPracticing dermatopathologists recruited from 40 US states participated in the 2-year REMI study and provided feedback on the MPATH-Dx version 1.0 tool. Independently, member dermatopathologists participating in an IMPSG workshop dedicated to the MPATH-Dx schema provided additional input for refining the MPATH-Dx tool. A reference panel of 3 dermatopathologists, the original authors of the MPATH-Dx version 1.0 tool, integrated all feedback into an updated and refined MPATH-Dx version 2.0.FindingsThe new MPATH-Dx version 2.0 schema simplifies the original 5-class hierarchy into 4 classes to improve diagnostic concordance and to provide more explicit guidance in the treatment of patients. This new version also has clearly defined histopathological criteria for classification of classes I and II lesions; has specific provisions for the most frequently encountered low–cumulative sun damage pathway of melanoma progression, as well as other, less common World Health Organization pathways to melanoma; provides guidance for classifying intermediate class II tumors vs melanoma; and recognizes a subset of pT1a melanomas with very low risk and possible eventual reclassification as neoplasms lacking criteria for melanoma.Conclusions and RelevanceThe implementation of the newly revised MPATH-Dx version 2.0 schema into clinical practice is anticipated to provide a robust tool and adjunct for standardized diagnostic reporting of melanocytic lesions and management of patients to the benefit of both health care practitioners and patients.

The presence of enlarged epithelioid/spindled nests located deep in the reticular dermis of a biphasic melanocytic neoplasm can mimic melanoma arising in a pre-existing nevus, causing over-interpretation of malignancy. We aimed to define the clinicopathologic significance of epithelioid/spindled nests in melanocytic nevi. Retrospectively using clinical and histologic information, we characterized 121 patients with a single lesion showing epithelioid/spindled melanocytes in the reticular dermis or subcutaneous fat, surrounded by melanophages, sometimes blending in with the adnexa. The majority of nevi occurred in women in the ages of 10 to 39 years, where the most frequent presentation was a changing mole. While 78% of the lesions displayed an anatomic (Clark's) level of IV-V, there was no ulceration, significant regression or inflammation. Up to 2 mitoses were found in only 12% of the cases, not correlating with the severity of cytological atypia. No recurrence or metastasis occurred during 45.5 months (mean) of clinical follow up in 26 patients. Notwithstanding the deep dermal extension, these findings suggest a benign histopathology and clinical outcome. Having compared the overlapping histopathology and clinical features between deep penetrating/clonal nevus and combined nevus, we posit that "inverted type-A nevus" might be considered a variant of the two.