Abstract

The distinction between true Spitz and conventional pathway tumors remains difficult given the recognition of morphologically Spitzoid neoplasms harboring conventional pathway mutations. However, their differing biological behavior underscores a critical need to define reproducible histopathologic criteria to distinguish them. Recent studies have highlighted the overlapping morphologic features of Spitz pathway melanocytic neoplasms and BRAF mutated and morphologically Spitzoid (BAMS) tumors. Here, we report a large series of thirty-eight BAMS tumors, including 10 cases with associated next-generation sequencing data. Most tumors harbor a BRAF V600E mutation (34/36) with single cases harboring BRAF V600K, BRAF G469E, and NRAS Q61R driver mutations. Patient ages varied widely from 6 to 69 years (mean 37). Most tumors developed on the limbs (lower extremity: 42% and upper extremity: 21%). Features common with Spitz pathway tumors include epithelioid morphology, clefting, cytologic atypia, and frequent epidermal induction. Distinguishing features of proliferations with a junctional component were pulverocyte morphology (19/22) while predominantly dermal proliferations were typified by distinct cell membranes (6/7). Kamino bodies were rare (5/29) and miniaturized when present. The majority of these tumors were reported with atypical or melanocytoma diagnoses (27/38), while four melanomas and seven nevi were also diagnosed. A more detailed description of the clinical and histopathologic features of BAMS will facilitate their recognition and the deployment of assays to assess for BRAF mutational status.