Case 113

A 54-year-old male with a gastric mass and an FNA was performed, here is the cell block:

1. What's your interpretation by morphology?

   A: inflammatory myofibroblast tumor

   B: gastrointestinal stromal tumor

   C: inflammation leiomyoma

   D: inflammatory fibrous polyp

Answer

the correct answer is B. This is a case of GIST.

Feature	A.Inflammatory Myofibroblastic Tumor (IMT)	B. Gastrointestinal Stromal Tumor (GIST)	C. Inflammatory Leiomyoma	D. Inflammatory Fibrous Polyp (IFP)
Histopathology	Spindle or myofibroblastic cells in a myxoid or collagenous stroma with prominent mixed inflammatory infiltrate (especially plasma cells). May be compact or fascicular	Spindle or epithelioid cells, often with skeinoid fibers; variable mitotic activity; minimal to marked pleomorphism	Well-circumscribed, bland spindle cells in fascicles with interspersed lymphocytes and eosinophils, sometimes mimicking IMT	Polypoid lesion with spindle or stellate fibroblasts, abundant eosinophils, prominent small vessels in edematous stroma
IHC	ALK+ (~50–60%) if ALK-rearranged; SMA+, desmin (focal+), cytokeratin (rare), calponin+	c-KIT (CD117)+, DOG1+, CD34+ (70–80%), SMA±, desmin−	SMA+, desmin+, caldesmon+, ALK−, CD34−, CD117−	CD34+, vimentin+, SMA−, S100−, CD117−, DOG1−
Molecular	ALK rearrangement (e.g., TPM3-ALK, RANBP2-ALK); also ROS1, NTRK3, RET fusions in ALK− IMTs	KIT or PDGFRA mutations (mutually exclusive); SDH-deficient GISTs lack these and have SDH mutations or epimutations	No recurrent genetic abnormalities; lacks ALK or KIT/PDGFRA mutations	PDGFRA mutations reported in some cases; no KIT mutations; no ALK rearrangement
Common Sites	Lung, abdomen, retroperitoneum, bladder, soft tissue	Stomach (60%), small bowel, colon, rectum, esophagus	Uterus most common (also GI tract, retroperitoneum)	Small intestine (ileum > jejunum), stomach, colon
Behavior	Intermediate (rare metastasis); may recur	Varies from benign to malignant based on site, size, mitotic rate	Benign	Benign

Reference: https://tumourclassification.iarc.who.int/chaptercontent/64/117

Case credit: UCSD Pathology

Author: Wangpan Jackson Shi, MD