Molecular Profile of Gastrointestinal Stromal Tumors in Sixty-Eight Patients from a Single Swiss Institution

Clinicopathological and mutational characteristics of primary double mutant gastrointestinal stromal tumor: a single center study with review of the literature

AIMS

Primary double KIT/PDGFRA mutations are very rare in gastrointestinal stromal tumours (GISTs) but have not been comprehensively studied to date. In the present study, we investigated the clinicopathologic and genetic features of eight cases of primary double-mutant GISTs, and we reviewed the literature.

METHODS AND RESULTS

The tumours occurred in six males and two females (age range 57-83 years) and involved the small intestine (n = 4), stomach (n = 2), rectum (n = 1) and retroperitoneum (n = 1). Clinical manifestations were variable, ranging from indolent (no symptoms) to aggressive disease (tumour rupture and haemorrhage). All patients underwent surgical excision, and six of them were treated with imatinib. No one experienced recurrence or other complications during the follow-up time (10 to 61 months). Histologically, all the tumours exhibited mixed cell types, accompanied by variable interstitial changes. KIT mutations were detected in all cases, and the majority of them were present in different exons (n = 5). No PDGFRA exon 12, 14 or 18 mutations were found. All the mutations were validated by next-generation sequencing, and two additional variants with comparatively low allelic fractions were identified in one case. Two of the cases had available allele distribution data, one with an in cis compound mutation and the other with an in trans compound mutation.

CONCLUSION

Primary double-mutant GISTs have distinctive clinicopathologic and mutational features. Studies of more cases are necessary for a better understanding of these tumours.

Small Gastric Stromal Tumors: An Underestimated Risk

BACKGROUND AND OBJECTIVES

Small gastrointestinal stromal tumors (GISTs) are defined as tumors less than 2 cm in diameter, which are often found incidentally during gastroscopy. There is controversy regarding the management of small GISTs, and a certain percentage of small GISTs become malignant during follow-up. Previous studies which used Sanger targeted sequencing have shown that the mutation rate of small GISTs is significantly lower than that of large tumors. The aim of this study was to investigate the overall mutational profile of small GISTs, including those of wild-type tumors, using whole-exome sequencing (WES) and Sanger sequencing.

METHODS

Thirty-six paired small GIST specimens, which were resected by endoscopy, were analyzed by WES. Somatic mutations identified by WES were confirmed by Sanger sequencing. Sanger sequencing was performed in an additional 38 small gastric stromal tumor samples for examining hotspot mutations in KIT, PDGFRA, and BRAF.

RESULTS

Somatic C-KIT/PDGFRA mutations accounted for 81% of the mutations, including three novel mutation sites in C-KIT at exon 11, across the entire small gastric stromal tumor cohort (n = 74). In addition, 15% of small GISTs harbored previously undescribed BRAF-V600E hotspot mutations. No significant correlation was observed among the genotype, pathological features, and clinical classification.

CONCLUSIONS

Our data revealed a high overall mutation rate (~96%) in small GISTs, indicating that genetic alterations are common events in early GIST generation. We also identified a high frequency of oncogenic BRAF-V600E mutations (15%) in small GISTs, which has not been previously reported.

New treatment strategies for advanced-stage gastrointestinal stromal tumours

When gastrointestinal stromal tumour (GIST), the most common form of sarcoma, was first recognized as a distinct pathological entity in the 1990s, patients with advanced-stage disease had a very poor prognosis owing to a lack of effective medical therapies. The discovery of KIT mutations as the first and most prevalent drivers of GIST and the subsequent development of the first KIT tyrosine kinase inhibitor (TKI), imatinib, revolutionized the treatment of patients with this disease. We can now identify the driver mutation in 99% of patients with GIST via molecular diagnostic testing, and therapies have been developed to treat many, but not all, molecular subtypes of the disease. At present, seven drugs are approved by the FDA for the treatment of advanced-stage GIST (imatinib, sunitinib, regorafenib, ripretinib, avapritinib, larotrectinib and entrectinib), all of which are TKIs. Although these agents can be very effective for treating certain GIST subtypes, challenges remain and new therapeutic approaches are needed. In this Review, we discuss the molecular subtypes of GIST and the evolution of current treatments, as well as their therapeutic limitations. We also highlight emerging therapeutic approaches that might overcome clinical challenges through novel strategies predicated on the biological features of the distinct GIST molecular subtypes.

Cytogenetic and molecular analyses of 291 gastrointestinal stromal tumors: site-specific cytogenetic evolution as evidence of pathogenetic heterogeneity

Gastrointestinal stromal tumor (GIST) is a mesenchymal neoplasm with variable behavior. An increased understanding of the tumor pathogenesis may improve clinical decision-making. Our aim was to obtain more data about the overall chromosome aberrations and intratumor cytogenetic heterogeneity in GIST. We analyzed 306 GIST samples from 291 patients using G-banding, direct sequencing, and statistics. Clonal chromosome aberrations were found in 81% of samples, with 34% of 226 primary tumors demonstrating extensive cytogenetic heterogeneity. 135 tumors had simple (≤5 changes) and 91 had complex (>5 changes) karyotypes. The karyotypically complex tumors more often were non-gastric (P < 0.001), larger (P < 0.001), more mitotically active (P = 0.009) and had a higher risk of rupture (P < 0.001) and recurrence (P < 0.001). Significant differences between gastric and non-gastric tumors were found also in the frequency of main chromosome losses: of 14q (79% vs. 63%), 22q (38% vs. 67%), 1p (23% vs. 88%), and 15q (18% vs. 77%). Gastric PDGFRA-mutated tumors, compared with gastric KIT-mutated, had a lower incidence of 22q losses (18% vs. 43%) but a higher rate of 1p losses (42% vs. 22%). The present, largest by far karyotypic study of GISTs provides further evidence for the existence of variable pathogenetic pathways operating in these tumors’ development.

The occurrence of gastrointestinal stromal tumors with second malignancies - Case series of a single institution experience

INTRODUCTION

Gastrointestinal stromal tumors (GISTs) may coexist with different types of malignancies, either synchronously or metachronously. The aim of this study was to characterize the clinical and histopathological features of GIST coexisting with other neoplasms.

METHODS

A retrospective analysis of 76 GISTs cases diagnosed at our institution between January 2003 and March 2020 was performed. A subgroup of cases with concomitant second malignancy was selected. The clinical and pathologic records were reviewed.

RESULTS

18 out of 76 patients (23.7%) with GISTs were diagnosed with the second neoplasms. In 11 cases GISTs were diagnosed metachronously to the second malignancy, whereas 7 cases of GIST were synchronous. The most common concomitant neoplasms were breast cancer and gastric cancer. The concomitant GIST were located mainly in small intestine (52.6%). 14 GISTs were classified as very low or low-risk (77.8%), 3 as moderate risk (16.7%) and 1 as high risk tumors (5.6%).

CONCLUSION

The coexistence of GIST with other malignancies may be more common, than it has been considered. As the most of concomitant GISTs occurs metachronously to the second malignancy, studying of this phenomenon requires a long-term follow-up.