Appendix - Gastrointestinal stromal tumors (GIST)

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Appendix

Other tumors

Gastrointestinal stromal tumors (GIST)

Reviewer: Jaleh Mansouri, M.D. (see Reviewers page)
Revised: 20 October 2012, last major update August 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.

General
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● 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
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● Partially obliterating nodules expanding appendiceal wall

Micro description
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● Spindle cell tumor, often with extracellular collagen globules (skenoid fibers)
● No atypia, no mitotic activity

Molecular description
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● One series with 2 appendiceal GISTS identified KIT mutations at exon 11 (Hum Pathol 2008;39:1252)

Positive stains
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● CD117, CD34 (often)

Negative stains
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● Alpha smooth muscle actin, S100

Differential diagnosis
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● Inflammatory fibrous polyp
● Leiomyosarcoma: actin+, desmin+
● Neurofibroma
● Schwannoma: often microtrabecular pattern with surrounding lymphoid cuff, S100+, CD117-, actin-

End of Appendix > Other tumors > Gastrointestinal stromal tumors (GIST)

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