The predominant growth pattern was fascicular in the spindle cell component (B), but focal areas with a slightly more epithelioid morphology had a trabecular growth pattern (C). In patient 2, there was a tumour-enteric fistula; the blue arrow denotes a loop of small intestine fistulising into the tumour. Kabeer Shah, 1,2 Andrew L Folpe, 1 Michael Miller, 3,4 Jeffrey A Morgan, 5 Chandrajit P Raut 6 & Leona A Doyle 3 1 Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN, 2 Department of Laboratory Medicine and Pathology, St Mary's Hospital, Madison, WI, 3 Department of Pathology, Brigham and Women's Hospital, Boston, MA, 4 Division of Genetics and Genomics, Boston Children's Hospital, Boston, MA, 5 Department of Medical Oncology, Dana Farber Cancer Institute, Boston, MA, and 6 Department of Surgery, Brigham and Women's Hospital, Boston, MA, USA Date of submission 12 June 2020 Accepted for publication 20 July 2020 Published online Article Accepted 22 July 2020 Shah K, Folpe A L, Miller M, Morgan J A, Raut C P & Doyle L A (2021) Histopathology 78, 281-289. https://doi.org/10.1111/his.14219 Aims: Blue naevi are uncommon dermal melanocytic neoplasms characterised by GNAQ/GNA11 mutations, which very rarely progress to melanoma. 31,33 Among non-melanocytic tumours, gastrointestinal stromal tumour, the most common mesenchymal neoplasm of the gastrointestinal tract, must be excluded, particularly in cases where melanin pigment is limited in extent. [Extracted from the article]