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Subspecialties Histology, Oncology, Cytology

Case of the Month

A 55-year-old woman presented with intermittent, non-radiating upper abdominal pain for five months. Abdominal CT revealed a 24x14 mm, well-defined, arterial phase-enhancing lesion in the head of the pancreas, diagnosed as gastrointestinal stromal tumor (GIST).

Which of the following is true of GISTs?

a. GISTs with KIT exon 9 mutations respond poorly to imatinib
b. 85 percent of GISTs are associated with KIT mutations
c. Small intestinal GIST has a more favorable prognosis than gastric GIST
d. GIST is not associated with NF1 mutations

Submitted by Vishnu Chandra Kumar Annadurai, Fellowship Trainee in Molecular Pathology; Thomas Alex Kodiatte, Professor; and Rekha Pai, Professor, Christian Medical College, Vellore, India.

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Ileal polyp. A) Hematoxylin and eosin 10x. Courtesy of Gang He.

Ileal polyp. B) hematoxylin and eosin 40x. Courtesy of Gang He.

Ileal polyp. C) positive synaptophysin immunohistochemistry. Courtesy of Gang He.

Ileal polyp. D) positive chromogranin A immunohistochemistry. Courtesy of Gang He.

a. Well-differentiated neuroendocrine tumor

Serotonin-producing neuroendocrine tumors are often described as “carcinoid.” Although the word “carcinoid” is used to characterize primary intestinal neuroendocrine tumors with clinicians, the term is considered obsolete (1). Endocrine tumors originate from enterochromaffin cells, which are neural crest cells of the intestinal crypts (2). Neoplasms exhibit various growth patterns including nest, trabeculae, glands, acini, and solidifications (3). Low-power view of this ileal specimen exhibits both glandular areas in a cribriform pattern and solidifications. High-power view demonstrates cytologic findings of nuclei with fine “salt and pepper” chromatin and prominent nucleoli.

According to the 2019 World Health Organization (WHO) classification criteria, well-differentiated tumors are classified as neuroendocrine tumors and defined as low, intermediate, or high-grade depending on the mitoses per 2 mm2 or Ki-67 percentage index (whichever is greater). Poorly differentiated lesions are termed neuroendocrine carcinoma (4).

Immunohistochemical staining for this biopsy with pan-endocrine markers (5) showed tumor cells strongly and diffusely positive for synaptophysin and chromogranin A. However, there was focal dim staining and negativity for neuron specific enolase and CD56, respectively. Antibody reactivity was negative for cytokeratin 7 and cytokeratin 20, decreasing the likelihood of adenocarcinoma of midgut or colorectal origin, respectively (6). The Ki-67 percentage index was less than 1 percent, supporting the morphologic diagnosis of a grade I well-differentiated neuroendocrine tumor.

Submitted by Erina McKinney, University of Kansas School of Medicine, Kansas City, Kansas; Gang He, American Diagnostic Consultation & Services, New York; and Ting Zhao, Department of Pathology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA

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  1. M Krishnan, F Tuma, “Intestinal Carcinoid Cancer” (2020). Available at:
  2. SN Pinchot et al., “Carcinoid tumors,” Oncologist, 13, 1255 (2008). PMID: 19091780.
  3. JY Kim, S-M Hong, “Recent updates on neuroendocrine tumors from the gastrointestinal and pancreatobiliary tracts,” Arch Pathol Lab Med, 140, 437 (2016). PMID: 27128301.
  4. ID Nagtegaal et al., “The 2019 WHO classification of tumours of the digestive system,” Histopathology, 76, 182 (2019). PMID: 31433515.
  5. T Terada, “Carcinoid tumors of digestive organs: a clinicopathologic study of 13 cases,” Gastroenterology Res, 2, 35 (2009). PMID: 27956948.
  6. H Takami et al., “Cytokeratin expression profiling in gastric carcinoma: clinicopathologic significance and comparison with tumor-associated molecules,” Pathobiology, 79, 154 (2012). PMID: 22286119.
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