Genetic and epigenetic alterations of SDH genes in patients with sporadic succinate dehydrogenase-deficient gastrointestinal stromal tumors.

This study aimed to investigate the association of SDH gene mutations and promoter methylation with succinate dehydrogenase-deficient gastrointestinal stromal tumors (SDH-deficient GISTs) and to further discuss the potential molecular mechanisms underlying SDHB expression loss in these tumors. First, a total of 26 patients with SDH-deficient GISTs were selected by identifying the loss of SDHB protein expression and wild-type for KIT and PDGFRa mutations. Then SDH gene mutations and promoter methylation were detected by DNA sequencing and methylation-specific polymerase chain reaction, respectively, and the clinical and pathological data of SDH-deficient GISTs patients were collected and analyzed accordingly. The results of genetic testing demonstrated that 38.46% (10/26) of these patients harbored mutations in SDHB, SDHC, and SDHD genes (3 cases with double mutations). Besides, aberrant promoter methylation of SDH genes was detected in 10 out of 26 cases (38.46%), including 8 cases in SDHA gene, 3 cases in SDHB gene, 1 case in both SDHA and SDHB genes. It is suggested that SDH gene mutations and promoter methylation may contribute to the loss of SDH protein expression in sporadic SDH-deficient GISTs. This study indicated that the genetic and epigenetic alterations of SDH genes may occur during tumor formation.

EGFR gene mutation in gastrointestinal stromal tumours.

AIMS: The aim of this study was to evaluate the mutation status of epidermal growth factor receptor (EGFR) in gastrointestinal stromal tumours (GISTs) and its association with various clinicopathological variables, as well as to discuss further the effects of EGFR mutations on tumour formation and progression. METHODS AND RESULTS: A well-characterized cohort of 323 GISTs, obtained between 2010 and 2015 from the surgical pathology files of at the Department of Pathology of the Nanjing Jinling Hospital, was screened for mutations in exons 19 and 21 of the EGFR gene. Patient clinical data and clinicopathological features were collected if available in the medical records. Among the 323 primary GISTs, we identified three cases (0.93%) of EGFR mutations; these mutations never occurred together with KIT, PDGFRα, KRAS or BRAF mutations. In two cases, tumour cells exhibited spindle cell morphology and, in one case, epithelioid cell morphology. Additionally, the morphology and immunophenotype of these three cases did not show significant differences compared to common GISTs. The clinical results in summary were that two cases of EGFR-mutated GISTs occurred in females and in the stomach. The mean age of EGFR-mutated cases was 54.33 years, and the follow-up data indicated that these tumours were low risk and exhibited low recurrence. CONCLUSIONS: We first established that GISTs carrying EGFR mutation are relatively benign tumours. Although EGFR mutations were rarely present in GIST, EGFR seems to play a significant role in the development and progression of GIST.

P16 overexpression in BRAF-mutated gastrointestinal stromal tumors.

BACKGROUND: The aims of this study were to analyze the histopathology, immunophenotype, molecular features, and prognosis in cases of BRAF-mutated gastrointestinal stromal tumors (GISTs) and to examine the p16 expression in these tumors, and further discuss its effects on tumor formation and progression. METHODS: In all, 283 GIST cases (201 KIT mutants, 12 PDGFRA mutants and 70 wild-type) from the 2010 to 2014 surgical pathology files of the Department of Pathology at Nanjing Jinling Hospital were analyzed for mutations in BRAF exon 15. Patient follow-up and clinical data were collected if available in the medical records. To determine the clinicopathological features and potential molecular mechanism, the authors examined 10 BRAF-mutated GIST cases for KIT, DOG1, SMA, desmin, S-100, Ki-67 and p16 expression. RESULTS: The authors identified 10 cases (3.5%) of BRAF (V600E) mutations in a series of 283 primary GISTs, without KIT (exons 9, 11, 13, 17) or PDGFRA (exons 12, 18) gene mutations. All 10 cases exhibited spindle-cell features, and the morphology and immunophenotype of these cases were no different from those in cases of KIT-mutated GISTs. The clinical results indicated that BRAF-mutated GISTs tended to occur more frequently in females (7/10), older individuals (mean age, 54.9 years) and the stomach (7/10), and that these tumors were low risk and exhibited low recurrence and mortality rates. Two different forms of p16 were identified, which presented with simultaneously strong and diffuse nuclear and cytoplasmic expression patterns. CONCLUSION: GISTs with the BRAF V600E mutation are relatively benign tumors with a distinctive molecular mechanism. The expression of the nuclear and cytoplasmic forms of p16 represent two independent mechanisms, and both seemed to control proliferation in response to oncogenic stimuli, protecting the cell from malignant transformation in BRAF-mutated GISTs.