Immunohistochemical examination showed coexpression of CD117 (c-kit) and CD34 in all independent GISTs and CD117 positivity in mast cells from the skin lesions.
Gastrointestinal stromal tumours (GISTs), once assumed to be of smooth muscle origin, generally express CD117 and CD34, similar to the interstitial cells of Cajal.
The IHC characteristic of GIST in descending order showed positivity for vimentin (88.9%), CD117 (83.3%), CD34 (77.8%), Ki67 (63.9%), SMA (38.9%), desmin (27.8%), and S100 (19.4%).
Approximately 70% of GISTs are positive for CD34, 20-30% are positive for smooth muscle actin (SMA), 10% are positive for S100 protein and <5% are positive for desmin.
The tumors differ from ordinary leiomyomas and schwannomas in several respects: the GISTs typically express c-kit protein (CD117) and CD34, 30% to 50% of them are (often focally) positive for alpha-smooth muscle actin, and all are negative for desmin and S100 protein.
<i>Materials and methods</i> We compared DNA methylation of 1,505 selected promoter CpGs in chronic myelogenous leukemia (CML), acute lymphoblastic leukemia (ALL) with and without the Philadelphia chromosome t(9:22), CD34+ hematopoietic stem cells transfected with <i>BCR-ABL</i>, and other tumors without <i>BCR-ABL</i> (acute promyelocytic leukemia (APL) and gastrointestinal stromal tumors (GIST).
The tumor was morphologically typical for a GIST, stained positively for CD34, and harbored an in-frame deletion (WK 557-558) in KIT exon 11 that is common in GISTs.
KIT-negative GISTs also showed lower expression rates of CD34, Bcl-2, and PKC than KIT-positive GISTs; mutational analysis revealed that 30% of KIT-negative GISTs harboured a PDGFRA exon 18 mutation.
Fine-needle aspiration biopsy revealed spindle cells with moderate pleomorphism and immunohistochemically reactive to CD117 and CD34 suggestive of GIST, but the clinical picture was unusual for GIST.
Although previous studies have shown that the clinical outcome of patients with GIST is associated with mitotic activity, the proliferation index determined by the Ki-67 labeling index, immunophenotype (CD34 and/or p53) and mutation in exon 11 of the c-kit, a definitive discrimination between benign and malignant GIST has not yet been established.
The first tumor was a submucosal gastric tumor and was diagnosed as a low-risk group GIST based on morphological characteristics and the results of an immunohistochemical analysis for c-kit and CD34.
Most GISTs (95%) express Kit (CD117), CD34 (70%), and heavy caldesmon (80%), whereas 25% are positive for smooth muscle actin and less than 5% for desmin.
Additional transcripts relevant to GIST biology were also evaluated, including members of the IGF-signaling pathway (IGF1, IGF2, and insulin receptor [INSR]), neural markers (CDH2[CDH: Cadherin], neurofilament, light polypeptide, LHX2 [LHX: LIM homeobox], and KIRREL3 [KIRREL: kin of IRRE like]), KIT, PDGFRA, CD34, and HIF1A.
Co-expression of KIT or CD34, which is also expressed in GIST and ICCs, was demonstrated in 18 (100%) and 16 SMemb-positive tumors (89%), respectively.
The percentage of CD34 positivity (38.8%) was low, in contrast with the high percentage of reactivity for SMA (77.8%) and S-100 (44.4%) in small intestine GISTs.