Abstract
Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. The most common localizations are the stomach and small intestine. About 95% of GISTs show KIT protein expression. Conventional chemotherapy and radiotherapy are not effective in treatment; thus, selective tyrosine kinase inhibitors are used. Since targeted molecular agents are employed in treatment, positron emission tomography/computed tomography (PET/CT) with F-18 fluorodeoxyglucose (FDG) is known to be very sensitive in assessing early response. It is known that progression-free survival is longer in-patient groups with an early response to treatment on F-18 FDG PET/CT. In cases where conventional radiologic imaging techniques are unclear in assessing disease progression, F-18 FDG PET/CT is also frequently used to detect recurrent disease. Metastases from malignant tumors of colorectal, ovarian, or gastric origin are often seen in the peritoneum. Primary peritoneal tumors (PPTs) are tumors that resemble stage III-IV serous ovarian carcinoma, originate from the peritoneum itself, are very rare, and have a very low survival rate. F-18 FDG PET/CT is recommended as the initial imaging modality in patients with suspected peritoneal mesothelioma (PM), which is one of the PPTs. F-18 FDG PET/CT also contributes with high sensitivity to the differential diagnosis of metastatic peritoneal carcinomatosis and PM. There are studies reporting that tumor metabolic response is correlated with progression-free survival in the assessment of treatment response in PM patients. This article discusses the role of molecular imaging methods in GISTs and PPTs.