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Micronodular PEComas of the appendix.

William J Anderson1, Nika Kojc2, Christopher D M Fletcher1

  • 1Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA.

Histopathology
|January 27, 2021
PubMed
Summary

This study reclassifies a rare appendiceal lesion as micronodular PEComa (perivascular epithelioid cell tumour). This distinct entity shows benign behavior and unique cellular markers.

Keywords:
PEComaappendicitisappendix

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Area of Science:

  • Gastrointestinal Pathology
  • Oncologic Pathology
  • Tumor Classification

Background:

  • Perivascular epithelioid cell tumours (PEComas) are rare, with appendiceal PEComas exceptionally infrequent.
  • Previous reports described a similar appendiceal lesion as 'granular degeneration of smooth muscle'.

Observation:

  • Three cases of a distinctive micronodular proliferation in the appendix were analyzed.
  • Histology revealed multifocal nodular proliferation of epithelioid cells with granular cytoplasm.
  • Immunohistochemistry showed positivity for muscle (SMA, desmin) and melanocytic markers (HMB45, melan A), along with cathepsin K and NKI-C3.

Findings:

  • The appendiceal lesion exhibits a unique immunophenotype, positive for both myogenic and melanocytic markers.
  • Electron microscopy identified structures consistent with pre-melanosomes.
  • The lesion, termed 'micronodular PEComa', appears to have an indolent course with no recurrence at 5 years in one case.

Implications:

  • This reclassification provides a more accurate designation for this appendiceal neoplasm.
  • Micronodular PEComa is distinct from other appendiceal lesions and tuberous sclerosis complex.
  • Understanding its characteristics aids in accurate diagnosis and management of rare gastrointestinal tumours.