An Update on Molecular Genetic Aberrations in Spitz Melanocytic Proliferations: Correlation with Morphological Features and Biological Behavior

Abstract

<p>The aim of the paper is to give an update on molecular genetic aberrations in Spitz melanocytic proliferations with special em- phasis on their correlation with morphological features and biological behavior. The Spitz group of melanocytic proliferations is defined by a combination of distinctive morphological features and driver molecular genetic events. Morphologically, these neoplasms are characterized by large, oval, polygonal, or spindled melanocytes with abundant eosinophilic cytoplasm, vesicular nuclei with prominent nucleoli, often in association with epidermal hyperplasia. Molecular aberrations in Spitz melanocytic proliferations can be divided into two main groups, according to the driver genetic change: 1) 11p amplification/HRAS muta- tion, present in about 20% of cases, and 2) kinase fusions, present in about 50%, further subdivided into tyrosine kinase fusions (ALK, ROS1, NTRK1, NTRK3, MET, RET) or serine-threonine kinase fusions (MAP3K8, BRAF). Driver genetic aberrations can be detected along the whole biological spectrum of Spitz melanocytic proliferations, and are mutually exclusive. Although driver genetic aberrations enable proliferation of melanocytes, additional genetic events (often biallelic inactivation of CDKN2A and TERT promoter mutations) are necessary for the development of overt Spitz malignancy.</p><p><strong>Conclusions</strong>. Recent studies have demonstrated that certain driver genetic aberrations are more often associated with the benign spectrum of Spitz melanocytic proliferations and indolent biological behavior (11p amplification/HRAS mutation, tyrosine kinase fusions). In contrast, some driver aberrations are more frequent in the atypical/malignant spectrum of Spitz melanocytic proliferations with a potential for aggressive biological behavior (serine-threonine kinase fusions). In addition, certain driver aberrations are often associated with distinctive morphological features. However, none of the morphological features is entirely specific for any of these driver genetic aberrations. Immunohistochemistry for ALK, ROS1, and pan-TRK can be used for screening purposes to detect cor- responding fusion proteins.</p>

Tumor-Type Agnostic, Targeted Therapies: BRAF Inhibitors Join the Group

“…In addition, rare BRAF gene fusions have been described in various cancer subtypes (frequency 0.3%), particularly in Spitzoid melanomas, pilocytic astrocytomas, papillary thyroid carcinomas, acinar pancreatic carcinomas, gastric carcinomas, serous ovarian carcinomas (both low-and highgrade), salivary gland carcinomas, and histiocytic neoplasms (pediatric and adult xanthogranulomas) (64)(65)(66)(67)(68)(69)(70)(71)(72)(73). BRAF gene fusions and point mutations have recently been found in a subset of adult and pediatric soft tissue tumors with spindle cell morphology and infantile fibrosarcoma-like growth pattern (74)(75)(76).…”

Genetic Studies on a Case of Eruptive Disseminated Spitz Nevus and Review of Other 33 Cases

“…57 Translocation involving tyrosine kinases are in fact evident in most of the Spitz neoplasias, involving ROS1, ALK, NTRK1, NTRK3, BRAF, RET, MAP3K8, or MET. 57,58 BRAF mutations have been considered as exclusive of Spitz nevus, and any Spitz-like melanocytic tumor with BRAF mutations should not be called a Spitz nevus but a Spitzoid tumor, spitzoid melanocytoma, atypical Spitz tumors, or malignant Spitz tumor (Spitzoid melanoma). In this sense, the current case is remarkable because the fusions which were examined for were absent in the lesions studied, despite the absence of BRAF mutations.…”