F-18 FDG PET/CT Assessment of Gastrointestinal Stromal Tumor Response to Sunitinib Malate Therapy

An extragastrointestinal stromal tumor in the omentum with peritoneal seeding mimicking an appendiceal mucinous cancer with carcinomatosis

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. These tumors tend to present most frequently in the stomach, followed by the small intestine. GISTs can also arise from the omentum, retroperitoneum, mesentery, or pleura and are termed extragastrointestinal stromal tumors (EGISTs) when they do so. EGISTs arising from the omentum are very rare. Due to the limited incidence of EGISTs in the omentum, the diagnostic criteria are not well established, and making a correct diagnosis may be difficult. In this report, we present a case of an EGIST of the omentum with peritoneal metastasis that was initially suspected to be an appendiceal mucinous carcinoma with carcinomatosis on positron emission tomography/computed tomography imaging.

Unusual features of gastrointestinal stromal tumor on PET/CT and CT imaging

Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor of the gastrointestinal tract. It can be benign or malignant in behavior. Stomach, being the most common site (70%) for GISTs, is followed by the small intestine (20%). Anorectal, colonic, and esophageal GISTs are uncommon, whereas extraintestinal GISTs are extremely rare. The presenting symptoms are highly dependent on tumor size and location, although a large number of GISTs are asymptomatic. The purpose of this article is to highlight the unusual characteristics of GISTs illustrated by PET/CT and CT imaging. These characteristics are organized into (1) unusual tumor location, (2) unusual clinical presentation, and (3) unusual sites of metastasis. Knowing the uncommon features of GISTs is important, as they are more often seen nowadays with the increasingly important role of PET/CT and CT in GIST management; and these tumors are associated with a poorer prognosis and unwanted delay in diagnosis is avoidable. With the availability of effective treatment by imatinib mesylate, a prompt and early diagnosis is essential for disease control. All GISTs illustrated in this article are pathologically proven.

Targeting both HIF-1 and HIF-2 in human colon cancer cells improves tumor response to sunitinib treatment

Sunitinib is an oral small-molecule multitargeted receptor tyrosine kinase inhibitor that has recently been shown to have clinical benefit as a single agent in renal cell cancer and gastrointestinal stromal tumors, leading to its Food and Drug Administration approval for treatment of these cancers. However, the benefit is short-lived; and for the majority of cancers, sunitinib single-agent clinical activity is low. Therefore, combination strategies with sunitinib are currently in clinical development. The hypoxia-inducible transcription factors, HIF-1 and HIF-2, induce gene programs important for cancer cell growth and angiogenesis. We hypothesized that inhibiting HIF-1 and HIF-2 would further improve tumor response to sunitinib therapy. To test this hypothesis, HIF-1α and HIF-2α genes were disrupted in colon cancer cells. We found that disruption of HIF-1α, HIF-2α, or both HIF-1α and HIF-2α genes led to improved tumor response to sunitinib. For xenografts in which both HIF-1α and HIF-2α genes were disrupted, there was prolonged complete remission with sunitinib treatment in 50% of mice. This enhanced response was mediated by two potential mechanisms. First, tumor angiogenesis and perfusion were almost completely inhibited by sunitinib when both HIF-1α and HIF-2α genes were disrupted. The enhanced inhibitory effect on tumor angiogenesis was mediated by the inhibition of multiple proangiogenic factors, including vascular endothelial growth factor and angiopoietin-like protein 4, and the induction of the antiangiogenic factor, thrombospondin 1. Second, disruption of HIF-1α, HIF-2α, or both HIF-1α and HIF-2α genes directly inhibited tumor cell proliferation. These preclinical findings have clinical implications and suggest novel clinical trials.