Appendix
Other tumors
Gastrointestinal stromal tumors (GIST)

Reviewer: Jaleh Mansouri, M.D. (see Authors page)

Revised: 1 March 2016, last major update August 2012

Copyright: (c) 2003-2016, PathologyOutlines.com, Inc.

PubMed Search: Gastrointestinal stromal tumor appendix
General
  • Very rare (only 4 cases at AFIP during 1970-1998, Am J Surg Pathol 2001 ;25:1433)
  • Mean age 56-72 years
  • Associated with appendicitis-like symptoms or incidental findings
  • No deaths due to primary appendiceal GIST, but appendix may also be site of metastases
  • Appear to follow indolent course although GIST with malignant features in appendix has been described (J Gastrointest Cancer 2010;41:9)
  • Gross Description
  • Partially obliterating nodules expanding appendiceal wall
  • Micro Description
  • Spindle cell tumor, often with extracellular collagen globules (skenoid fibers)
  • No atypia, no mitotic activity
  • Molecular / Cytogenetics Description
  • One series with 2 appendiceal GISTS identified KIT mutations at exon 11 (Hum Pathol 2008;39:1252)
  • Positive Stains
  • CD117, CD34 (often)
  • Negative Stains
  • Alpha smooth muscle actin, S100
  • Differential Diagnosis
  • Inflammatory fibrous polyp
  • Leiomyosarcoma: actin+, desmin+
  • Neurofibroma
  • Schwannoma: often microtrabecular pattern with surrounding lymphoid cuff, S100+, CD117-, actin-