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Discerning Merkel Cell Carcinoma from Other Tumors

Am J Dermapathol; ePub 2018 Jul 24; Bandino, et al

The presence of a trabecular pattern helps to differentiate Merkel cell carcinoma (MCC) from other small round blue cell (SRBC) tumors, and specificity approaches that achieved with immunostaining, a recent study found. Researchers conducted a retrospective, institutional review, board–approved, observational study on microscopic images of 79 MCCs and 74 other SRBC tumors. An expert dermatopathologist evaluated blinded and randomized microscopic specimens and recorded histologic patterns (diffuse, infiltrative, large anastomosing nests, small islands, any trabecular, focal trabecular, mixed trabecular, and predominately trabecular). They found:

  • Trabecular features were identified in >72% of MCCs but only rarely in non-MCC SRBC tumors.
  • The presence of any amount of a trabecular pattern favored a diagnosis of MCC over SRBC tumors with a sensitivity of 72.2% and a specificity of 87.8%.
  • If “any” and “focal” trabecular patterns were discounted, specificity rose to 93.2%.

Bandino J, Purvis C, Shaffer B, Gad A, Elston DM. A comparison of the histopathologic growth patterns between non-Merkel cell small round blue cell tumors and Merkel cell carcinoma. [Published online ahead of print July 24, 2018]. Am J Dermapathol. doi:10.1097/DAD.0000000000001232.