Fig. 2

Clinical, dermoscopic, and pathologic characterizations of the skin tumors examined. For A-D, the BIMT examined was located on the back of the patient’s hand. a Clinical image of a skin-colored, raised tumor. b Dermoscopy image (20× magnification) shows a hypopigmented structureless area and discrete linear vessels at the periphery of the tumor. c Histology shows an intradermal, symmetrical, and well-delineated nodular melanocytic proliferation (hematoxylin & eosin (H&E), 20×) with no pigmentation. d At a higher magnification (200×), histology shows the lesion presents as a large, isolated group of atypical eosinophilic epithelioid cells with enlarged nuclei and abundant pink cytoplasm intermingled with smaller mature melanocytic cells (H&E). No mitosis or necrosis is observed. Clear and vacuolated cells represent adipocyte metaplasia. These findings are compatible with a diagnosis of BIMT. Loss of BAP1 expression and BRAF V600E positivity were detected in the melanocytes by IHC (data not shown). For E-H, the BIMT examined was located on the back torso of the patient. e Clinical image of a reddish-brown, dome-shaped papule. f Dermoscopy image (20× magnification) shows a central, hypopigmented structureless area surrounded by clustered brown irregular globules which vary in shape and size. g Histology shows a melanocytic lesion with typical junctional nests and a predominant intradermal, well-delineated nodular melanocytic proliferation. Moderate pigmentation and adipocyte metaplasia are also observed (H&E, 20× magnification). h At higher magnification, histology of the intradermal component (H&E, 200× magnification) shows large epithelioid cells intermingled with smaller mature melanocytic cells, compatible with a BIMT. IHC demonstrated a loss of BAP1 expression in the large cells (data not shown). Next generation sequencing additionally revealed the presence of a BRAF gene mutation (p.V600E). For I-L, the melanoma examined was located on the front torso of the patient. i Clinical image of a flat pigmented lesion (indicated with black arrow). j Dermoscopy image (20× magnification) shows a peripheral fine reticular network, a central brown homogenous area, irregularly distributed brown globules, and a small depigmented area. k Histology shows a compound, asymmetrical melanocytic lesion. The junctional component is characterized mostly by the spread of single atypical cells with upward migration, while the intradermal component includes both aggregated and diffuse cells with foci of adipocyte metaplasia (H&E, 20× magnification). l At higher magnification (H&E, 200×), the intradermal component is found to be composed of a large population of isolated eosinophilic epithelioid cells intermingled with smaller mature melanocytic cells. The junctional component presents a predominant lentiginous spread of large atypical epithelioid cells with pagetoid migration. The lesion is classified as an in situ melanoma associated with a background of BIMT. Sequencing further revealed this lesion as being BRAF wild-type