La tumeur de Spitz et le mélanocytome épithélioïde pigmenté : de nouveaux cadres nosologiques pour des tumeurs souvent mal définies

Simulants of Malignant Melanoma

During the recent period, dermoscopy has yielded improvement in the early disclosure of various atypical melanocytic neoplasms (AMN) of the skin. Beyond this clinical procedure, AMN histopathology remains mandatory for establishing their precise diagnosis. Of note, panels of experts in AMN merely report moderate agreement in various puzzling cases. Divergences in opinion and misdiagnosis are likely increased when histopathological criteria are not fine-tuned and when facing a diversity of AMN types. Furthermore, some AMN have been differently named in the literature including atypical Spitz tumor, metastasizing Spitz tumor, borderline and intermediate melanocytic tumor, malignant Spitz nevus, pigmented epithelioid melanocytoma or animal-type melanoma. Some acronyms have been further suggested such as MELTUMP (after melanocytic tumor of uncertain malignant potential) and STUMP (after Spitzoid melanocytic tumor of uncertain malignant potential). In this review, such AMN at the exclusion of cutaneous malignant melanoma (MM) variants, are grouped under the tentative broad heading skin melanocytoma. Such set of AMN frequently follows an indolent course, although they exhibit atypical and sometimes worrisome patterns or cytological atypia. Rare cases of skin melanocytomas progress to loco regional clusters of lesions (agminate melanocytomas), and even to regional lymph nodes. At times, the distinction between a skin melanocytoma and MM remains puzzling. However, multipronged immunohistochemistry and emerging molecular biology help profiling any malignancy risk if present.

Spindle cell melanocytic lesions: part II—an approach to intradermal proliferations and horizontally oriented lesions

Melanocytic lesions show great morphological diversity in their architecture and the cytomorphological appearance of their composite cells. Whereas functional melanocytes show a dendritic cytomorphology and territorial isolation, lesional nevomelanocytes and melanoma cells typically show epithelioid, spindled or mixed cytomorphologies, and a range of architectural arrangements. Spindling is common to melanocytic lesions, and may either be a characteristic feature or a divergent appearance. The presence of spindle cells may mask the melanocytic nature of a lesion, and is often disconcerting, either due to its infrequent appearance in a particular lesion or its interpretation as a dedifferentiated phenotype. Spindle cell melanocytic lesions follow the full spectrum of potential biological outcomes, and difficulty may be experienced judging the nature of a lesion due to a lack of consistently reliable features to predict biological behaviour. Over time, recognition of numerous histomorphological features that may portend a more aggressive lesion have been identified; however, the translation of these features into a diagnostic entity requires a gestalt approach. Although most spindle cell melanocytic lesions may reliably be resolved through this standard approach, problem areas do exist for the surgical pathologist or dermatopathologist. With this review (part II of II), we complete our discussion of spindle cell melanocytic lesions, in order to: (1) model a systematic approach to such lesions; and (2) provide familiarity with those melanocytic lesions which either typically or occasionally display a spindled cytomorphology.