Population-Based Epidemiology and Mortality of Small Malignant Gastrointestinal Stromal Tumors in the USA

BACKGROUND AND AIMS

Gastrointestinal stromal tumors (GISTs) have significant variability in size and malignant behavior. Our current understanding is limited to pathological analyses, autopsy studies, and small case series. The aim of the current study is to define the risk factors, incidence, and mortality rates of GIST <2 cm in the National Cancer Institute's Surveillance, Epidemiology, and End Results database.

METHODS

Patients with histologically confirmed malignant GIST <2 cm were studied from 2001 to 2011. GIST was defined by GI tumor site codes and GIST-specific histology codes.

RESULTS

We identified 378 patients with GIST <2 cm. The average age at diagnosis was 64.0 years with equal sex distribution. The most common tumor location was the stomach (62.2 %), followed by the small intestine (23.3 %), colon (5.6 %), and rectum (3.4 %). Most patients had localized disease (79.4 %), but 11.4 % had regional/distant metastatic disease. The annual incidence rate was 4.2 per 10,000,000 (10M). This was the highest among Blacks (7.6 per 10M). Among patients with GIST and no additional cancers, the 5-year GIST-specific mortality was 12.9 %. Moreover, there was a significantly increased 5-year GIST-specific mortality in those patients who had regionally advanced (34.0 %) or metastatic GIST (34.3 %), as compared to those patients with localized GIST (5.6 %).

CONCLUSIONS

This study represents the first population-based analysis of malignant GIST <2 cm. While quite rare, these tumors have an underappreciated disease-specific mortality. Further studies are needed to define the underlying reasons for the identified racial differences, to develop novel risk assessment schema for patients with these small tumors, and to determine appropriate indications for resection and/or medical therapy.

Long segmental hyperplasia of interstitial cells of Cajal with giant diverticulum formation

Sporadic gastrointestinal stromal tumors (GISTs) usually form a well-circumscribed mass. In contrast, diffuse interstitial cell of Cajal (ICC) hyperplasia along the Auerbach plexus without a discrete mass may occur in patients with germline mutations in the NF1, c-KIT or PDGFRA genes. However, sporadic, diffuse ICC hyperplasia without c-KIT or PDGFRA mutations has not been reported. We describe herein one such case, forming a giant diverticulum. A 63-year-old woman with no features of Neurofibromatosis 1 (NF1) presented with increasing abdominal pain for more than 30 years. A large, diverticulum-like mass in the ileum was resected. Microscopically, a diffuse proliferation of bland spindle cells was seen extending for 12 cm, replacing the muscularis propria and lined by intact mucosa. The spindle cells were CD117+/CD34+/DOG1+/SMA+/Desmin-/S100-. Mutation analyses did not reveal any mutations in c-KIT or PDGFRA. The lesion had two silent mutations in the NF1 gene. It is rare of the diffuse form of sporadic ICC hyperplasia showing diffuse longitudinal microscopic growth completely replacing the muscularis propria, mimicking diffuse ICC hyperplasia in hereditary GIST syndromes, but without solid components and no c-KIT or PDGFRA gene mutations. This peculiar form of sporadic ICC hyperplasia may be related to intestinal dysmotility in this ileal segment and giant diverticulum formation.

Sporadic segmental Interstitial cell of cajal hyperplasia (microscopic GIST) with unusual diffuse longitudinal growth replacing the muscularis propria: differential diagnosis to hereditary GIST syndromes

Gastrointestinal stromal tumors (GIST) usually form a well-circumscribed mass. However, patients with germline mutations in c-KIT, PDGFRA and NF1 may present with diffuse interstitial cell of Cajal (ICC) hyperplasia along the Auer-bach plexus without forming a discrete mass. To our knowledge, sporadic diffuse ICC hyperplasia replacing the gut wall has not been described previously. We describe herein two such cases. Case 1 was a 59-yr-old woman who presented with signs of ileus and a large mass submitted as Meckel diverticulum. The resection specimen showed a large GIST with diverticulum-like and solid areas. The diverticular component showed a diffuse proliferation of spindle cells extending for several centimetres from the solid tumor replacing the full thickness of the gut wall and lined by intact mucosa. Mutation analysis revealed a combined deletion/insertion in c-KIT exon 11 (V560delEins) in both the solid and the diffuse tumor component. Case 2 was a 66-yr-old man who underwent segmental sigmoid colon resection for adenocarcinoma in a villous adenoma. Random sections from grossly unremarkable colonic wall showed a diffuse proliferation of CD117+/CD34+ spindle cells completely replacing the muscularis propria for a length of 6 mm. Molecular analysis revealed a somatic point mutation/ deletion in exon 11 of c-KIT (Q575L; L576_W582del). Absence of multiple lesions and demonstration of a wild-type sequence for c-KIT in surrounding normal tissue ruled out the possibility of a germline mutation in both cases. This peculiar diffuse form of sporadic ICC hyperplasia results from somatic c-KIT mutations and must be distinguished from syndromic ICC hyperplasia associated with hereditary GIST syndromes.