The patient is a 64 - year - old Asian man, he was admitted to a local hospital for dizziness and anemia the past year ,Computed tomography scan disclosed one large tumor at the bottom of the stomach(FIG1A,1B), Subsequently, the endoscopic biopsy was performed, and the pathological diagnosis was “Gastrointestinal stromal tumors”. The little tumor tissue was positive for CD117 and Dog-1 by immunohistochemical (IHC) stains,but negative for S100,SMA,Desmin,PCK,CK5/6,P63,P40,CK20 and CDX-2,Due to the large size of the tumor, the patient did not receive immediate surgical treatment, but began taking imatinib(400mg,qd),11months later, the patient was admitted to the local hospital for dizziness and fever, and then transferred to our hospital for further diagnosis and treatment. The outpatient diagnosis was "gastric stromal tumor with hemorrhage and anemia". Computed tomography scan disclosed the gastric wall of the fundus was significantly thickened, and a large mass with a size of 11.7cm×0.7cm was seen inside. The shape of the lesion was irregular, the edges of enhanced scanning were significantly enhanced, and large flaked areas of unenhanced liquefaction necrosis could be seen in the center(FIG2A,B). Then he underwent surgical treatment in our hospital, During the operation, the primary tumor was found to be located at the bottom of the stomach and grew out of the luminal cavity, involving the diaphragm and the tail of the pancreas. the gastric tumor, spleen and pancreas were removed, and the postoperative pathological diagnosis and genetic testing were performed. After the pathological diagnosis, imatinib administration was initiated (400 mg/d) at a few days after the operation, two months after the operation, the patient is alive with an outpatient status. At present, there are no serious postoperative complications.
2.1 Materials and methods
2.1.1 Immunohistochemical analysis
The surgical specimen was examined grossly and fixed in 10% neutral formalin. The representative specimen was embedded in paraffin and submitted for permanent histological examination.Four-micron thick hematoxylin and eosin (H&E) stained sections were prepared.
Immunohistochemical stains for CD117 (mouse monoclonal,Abcam), CD34 ( mouse monoclonal, Ventana), DOG-1 ( rabbit monoclonal, Ventana), smooth muscle actin (SMA) (clone 1A4, mouse monoclonal, Ventana), CD68(mouse monoclonal,Abcam),S-100(mouse monoclonal,Abcam),and Ki-67(mouse monoclonal,Abcam) were performed by an automated immunostainer .
2.1.2 Sequence analysis of the c-kit and PDGFRα gene
For mutational analysis,the paraffin-embedded sections of the patients' tumors were sent to guangzhou microread medical laboratory for detection of gene mutations associated with individualized treatment of tumors,the tissues examined included typical gastric stromal tumor and dedifferentiated pleomorphic sarcoma.The genomic DNA was extracted from paraffin-embedded sections of tumor tissue by using sureselect human all exon V6(Agilent,America),Genes (exons) analyzed include the following [Gene(exon)]:C-kit(9,11,13,17)and PDGFRα(12,18),The test was performed with the patient's informed consent.
2.2 Results
2.2.1 Histopathology and immunohistochemistry
The resection specimens showed that the tumor had separated from the gastric tissue. The size of the tumor was 15×11×4.5cm.The cut surface was grayish white and the local area was gray-red, localized bleeding and necrosis can be seen on the incised surface.The tumor affected the spleen and pancreatic tissues. The gastric wall thickened to 1.1 cm immediately adjacent to the resection margin of esophagus, and the gastric mucosal surface at the thickening point is slightly rough. Microscopically, the tumor is composed of two distinct demarcated areas; one conventional GIST area and the other dedifferentiated area. The classic area consists mostly of epithelioid cells and spindle cells of uniform size, abundant cytoplasm, and rare nuclear pleomorphism. The tumor cells in classic GIST area was positive for CD117 (Fig. 3A),CD34 (Fig. 3B) and Dog-1(focally,Fig. 3C) by immunohistochemical (IHC) stains. In particular, the dedifferentiated pleomorphic sarcoma component was found locally in the tumor, abruptly adjacent to the classical GIST. These pleomorphic cells are of various sizes, with large, hyperchromatic nuclei and prominent nucleoli, among which are bizarre multinucleated giant cells(FIG,4). At higher magnification abnormal mitosis are easy to find. The undifferentiated pleomorphic sarcoma of the tumor was positive for SMA(not shown),but negative for CD117 (Fig. 5A), CD34(Fig5B), DOG-1 (Fig. 5C), desmin (not shown), CD68(not shown),andS-100(not shown)by IHC stains. Notably, there was a loss of CD117and CD34 expression in the undifferentiated component of the tumor.
The resected pancreas, spleen and adrenal gland were involved by the tumor cells, and the live tumor showed a highly cellular and aggressive growth pattern.
Additionally, sarcomatoid tumor cells had higher mitotic activity by immunostain for proliferative index Ki-67 compared to adjacent classic epithelioid GIST tumor cells(FIG,6),indicating higher mitotic activity. The resection margins were negative.After imatinib treatment, some areas of hyaline degeneration are seen in the tumor tissue(Fig. 7A).
2.2.2 Mutational status of the patient
We detected the exon 9/11/13/17 of c-kit and the exon 12/18 of PDGFRα gene, the patient's genetic test results showed that the exon 11 of c-kit gene was homozygous deficient(FIG8), and the codon 567 at the exon 12 of PDGFRα homozygous mutation (Pro567=,CCA>CCG)(Fig9).There was no gastric stromal tumor in the immediate family. C-kit gene mutation is related to the efficacy of targeted therapy with imatinib, this test detected the 11 exon deletion mutation of c-kit gene. Patients with this mutation were more sensitive to imatinib treatment than patients with 9 exon mutation, and the treatment effect was the best.