Fig. 5: Architectural and cytologic features of melanocytic tumors with MYH9-NTRK3 fusion.

a At scanning magnification, case 2 is intradermal with a nodular configuration and extends into the subcutis. b There is “honeycomb” pattern of infiltration into the subcutis and “collagen trapping” at periphery of the tumor. c Constituent melanocytes are moderately large and epithelioid arranged syncytially. d Low-power view of case 22 shows an intradermal tumor. Markedly desmoplastic stroma displaces the elastotic material in the superficial dermis. e Melanocytes are arrayed as small aggregates and single cells intercalating between thickened collagen bundles. There is infiltrative growth pattern around eccrine glands and arrector pili muscle. f. Epithelioid melanocytes have well-defined cellular membranes.