Novel oncogene and tumor suppressor mutations in KIT and PDGFRA wild type gastrointestinal stromal tumors revealed by next generation sequencing.

Among gastrointestinal stromal tumors (GISTs) of 10-15% are negative for KIT and PDGFRA, and most of these cases are SDH deficient. Recent studies have provided data on additional molecular alterations such as KRAS in KIT mutant GISTs. We aimed to assess the frequency and spectrum of somatic mutations in common oncogenes as well as copy number variations in GISTs negative for KIT and PDGFRA mutations. GISTs with wild type KIT/PDGFRA were tested via next generation sequencing for somatic mutations in 341 genes. SDHB immunohistochemistry to evaluate for SDH deficiency was also performed. Of 267 GISTs tested for KIT and PDGFRA mutations, 15 were wild type, of which eight cases had material available for further testing. All eight cases had loss of SDHB expression and had various molecular alterations involving ARID1A, TP53, and other genes. One case had a KRAS G12V (c.35G>T) mutation in both the primary gastric tumor and a post-imatinib recurrence. This tumor had anaplastic features and was resistant to multiple tyrosine kinase inhibitors, ultimately resulting in cancer-related mortality within 2 years of diagnosis. In conclusion, KRAS mutations occur in rare GISTs with wild type KIT and PDGFRA. These tumors may display immunohistochemical positivity for KIT and primary resistance to tyrosine kinase inhibitors.

Additional Primary Malignancies in Patients with Gastrointestinal Stromal Tumor (GIST): A Clinicopathologic Study of 260 Patients with Molecular Analysis and Review of the Literature.

BACKGROUND: The incidence of other primary neoplasms in gastrointestinal stromal tumor (GIST) patients is relatively high. Our aim was to better characterize the clinicopathologic and molecular relationships in a cohort of GIST patients. METHODS: All GIST patients with tumor samples sent for molecular testing were identified via electronic medical records. Clinicopathologic characteristics of GIST and additional primary malignancies were analyzed. RESULTS: Of 260 patients, 50 (19 %) had at least one additional primary malignancy. In 33 patients, separate primary neoplasms predated their GIST diagnosis and most commonly included: prostate (n = 9), breast (n = 8), and hematologic (n = 5). Renal (n = 4) and hematologic (n = 3) malignancies were the most frequent cancers identified after GIST diagnosis. The majority (8 of 12, 66 %) of malignancies diagnosed after GIST were found incidentally. Patients who developed other malignancies after GIST more often had KIT exon 11 mutations (100 vs. 66 %, P = 0.01). In comparison to patients with only GIST, patients with a second primary neoplasm of any chronology had GISTs with increased mitotic rate (≥5 per 50 high-power fields) (P = 0.0006). Literature review revealed colorectal cancer, gastric, prostate, renal, leukemia, and desmoid-type fibromatosis as the most common secondary neoplasms. CONCLUSIONS: Nineteen percent of GIST patients develop other malignancies. This is the first report to describe a relationship between additional primary malignancy and both mutation and mitotic rate of GIST. Although the basis of these relationships remains to be investigated, caution in the clinical management of GIST patients with additional lesions is warranted.

Intramuscular corpora amylacea adjacent to ileal low-grade neuroendocrine tumours (typical carcinoids): a light microscopic, immunohistochemical and ultrastructural study.

AIMS: The purposes of this study are to (1) document the prevalence of intracytoplasmic inclusions adjacent to ileal well-differentiated neuroendocrine tumours (WNETs), (2) examine whether and how tumour and patient characteristics are associated with inclusions and (3) investigate their properties on special stains and electron microscopy in comparison with corpora amylacea (CA). METHODS: We examined the resection slides from 26 ileal, 5 gastric and 5 rectal cases of WNET. Inclusions were readily identified with H&E staining. Histochemical, immunohistochemical and ultrastructural evaluations were performed on the block with the highest number of inclusions. RESULTS: Intracytoplasmic inclusions occurred adjacent (<1 mm) to 15 of 26 (57.7%) ileal WNETs. Patients with and without inclusions were of similar mean ages (59.5 vs 57.4 years; p=0.88), but NETs with inclusions were larger than those without inclusions (3.3 vs 1.7 cm, p=0.03). Inclusions were neither associated with gastric (mean age=65 years, mean diameter=1.5 cm) or rectal WNETs (mean age=47.8 years, mean diameter=0.5 cm) (p=0.01), nor were they present >1 mm from ileal NETs. CA stained strongly for ubiquitin, DPAS and Alcian blue; faintly and peripherally for desmin and smooth muscle actin and negatively for calcium. Ultrastructurally, their appearance was consistent with filaments, some with cores of particle matter. CONCLUSIONS: Our results suggest that these inclusions are virtually identical to CA and present adjacent to the majority of ileal WNET. They may be the result of a degenerative process, possibly due to chronic myocyte stress from an infiltrating slow growing tumour mass or local hormonal effects.

Corpora amylacea in gastrointestinal leiomyomas: a clinical, light microscopic, ultrastructural and immunohistochemical study with comparison to hyaline globules.

CONTEXT: Corpora amylacea (CA) are inclusions with starch-like composition that occur in various conditions. We have observed CA in gastrointestinal leiomyomas (GILM) and hypothesised that they differ from intracytoplasmic hyaline globules (HG) of GILM. We aimed to investigate the anatomical distribution, prevalence, staining characteristics and ultrastructural features of CA and compare them with HG of GILM. DESIGN: Slides from a consecutive series of resected GILM and bland spindle cell tumours were examined for CA and HG. Special stains, electron microscopy and elemental analysis were performed on select leiomyomas. RESULTS: CA occurred in 13/35 GILM (37%) from the following sites: oesophagus (4/8), stomach (5/7) including one frozen section, small intestine (1/2) and large intestine (3/18), but were not identified in 19 gastrointestinal stromal tumours (12 gastric, 7 small intestinal; p=0.0019), five schwannomas (three gastric, two small intestinal; p=0.154) and 35 non-GILM (p=0.0001). The densities of CA ranged from one per 4-200 mm(2). CA stained intensely with periodic acid Schiff after diastase predigestion (PASD), Alcian blue and ubiquitin, and faintly in peripheral zones for desmin and smooth muscle actin. Ultrastructurally, CA consisted of an electron-dense outer layer and a fibrillar core with scattered particle matter. HG were present in all leiomyomas, but showed variable staining for PASD, negative staining for Alcian blue and ubiquitin, and positive staining for smooth muscle markers. CONCLUSIONS: CA are a distinctive histological feature of approximately one third of GILM with different composition to HG. These differences may represent divergent degenerative processes or different stages of a single degenerative process over time.

Promyelocytic leukemia zinc finger and histone H1.5 differentially stain low- and high-grade pulmonary neuroendocrine tumors: a pilot immunohistochemical study.

Promyelocytic leukemia zinc finger is a zinc finger transcription factor that functions as a transcriptional repressor. Its expression has been shown to be down-regulated in hematopoietic, melanocytic, and mesothelial malignancies. Histone H1.5 is a variant of histone H1, a family of linker proteins that organizes chromosomes into higher order structures. Its function is of key importance in gene expression and has been linked to more aggressive forms of prostatic carcinoma. This study aimed to investigate the immunohistochemical detectability of promyelocytic leukemia zinc finger and histone H1.5 in pulmonary neuroendocrine tumors, comprising 11 carcinoid tumorlets, 24 typical carcinoids, 12 atypical carcinoids, 20 small cell carcinomas, 11 large cell neuroendocrine carcinomas, and 2 combined small cell carcinomas-large cell neuroendocrine carcinomas. Promyelocytic leukemia zinc finger immunohistochemistry revealed moderate or strong nuclear staining in all carcinoid tumorlets, 23 of 24 typical carcinoids, and 7 of 12 atypical carcinoids in contrast to 9 of 11 large cell neuroendocrine carcinomas, all small cell carcinoma, and both combined small cell carcinoma-large cell neuroendocrine carcinomas, which showed no nuclear immunoreactivity. Histone H1.5 immunohistochemistry revealed only focal or no immunoreactivity in all carcinoid tumorlets and 19 of 24 typical carcinoids, whereas 7 of 12 atypical carcinoids, 19 of 20 small cell carcinomas, 10 of 11 large cell neuroendocrine carcinomas, and both combined small cell carcinomas-large cell neuroendocrine carcinomas displayed positive (≥ 10%) nuclear immunoreactivity-ranging from a minority of weak staining to a majority of strong staining cases. Our data suggest that the relative expression ratios of promyelocytic leukemia zinc finger and histone H1.5 may correlate with grade of pulmonary neuroendocrine tumors. Immunohistochemical stains for these markers, especially on small biopsies with crush artifact, may prove to be diagnostically useful.

Intraductal polypoid lipid-rich neuroendocrine tumor of the pancreas with entrapped ductules: case report and review of the literature.

Pancreatic neuroendocrine tumors of the main pancreatic duct are rare and usually small due to symptoms of pancreatic duct obstruction. We present a case of a large (3 cm), well-differentiated (G1) lipid-rich polypoid neuroendocrine tumor of the pancreas completely occluding the main pancreatic duct with non-neoplastic-entrapped ductules and CK19 positivity. Clinical, radiological, gross, microscopic, immunohistochemical, and ultrastructural findings are discussed. The literature pertaining to the unique features of this case is reviewed including clinical and pathologic pitfalls and the possible etiologic and prognostic significance of these findings.