Value of FDG-PET/CT examinations in different cancers of children, focusing on lymphomas.

The aim of the study was to assess sensitivity and specificity of FDG-PET/CT in different forms of childhood cancer. We retrospectively evaluated the results dedicated of 162 FDG-PET/CT examinations of 86 children treated with: Hodgkin lymphoma (HL; n = 31), non-Hodgkin lymphoma (NHL; n = 30) and other high grade solid tumors (n = 25). Patients were admitted and treated in two departments of pediatric hematology and oncology in Hungary. FDG-PET/CT was performed for staging (n = 25) and for posttreatment evaluation (n = 137). Imaging was performed in three FDG-PET/CT Laboratories, using dedicated PET/CT scanners. False positive results were defined as resolution or absence of disease progression over at least 1 year on FDG-PET/CT scans without any intervention. In some cases histopathological evaluation of suspicious lesions was performed. Fals negative results were defined as negative FDG-PET/CT results in case of active malignancy. Positive predictive values (PPV) and negative predictive values (NPV) were calculated. NPV was 100%. The highest PPV was observed in high grade solid tumors (81%), followed by HL (65%) and NHL (61%). There was a major difference of PPV in different histological types of HL (50% in HL of mixed-cellularity subtype, 90% in nodular sclerosing, and 100% in lymphocyte-rich and lymphocyte depleted HL). We treated one patient with nodular lymphocyte predominant HL, who had 5 false positive FDG-PET/CT results. PPV of T- and B-lineage NHL were similar (60% and 62%, respectively). We observed an interesting difference of PPV in different stages of HL and NHL. In HL PPV was higher in early than in advanced disease forms: 66% in stage II HL and 60% in stage III HL, whereas there was an inverse relationship between PPV and disease stages in NHL 0% in stage I and II patients, 67% in stage III and 100% in stage IV patients. PPV was lower in males (54%) than in females (65%). PPV were 64% vs. 58% in patients under vs. over 10 years of age. Negative FDG-PET/CT results during follow-up reliably predict the absence of malignancy. Positive FDG-PET/CT scan results in general have a low PPV. The relatively high PPV in patients with histologically proven high grade solid tumors, advanced stages of NHL and with nodular sclerosing, lymphocyte-rich and lymphocyte depleted subtypes of HL warrant a confirmation by biopsy, whereas the watch-and-wait approach can be used in other forms of childhood cancer patients with a positive FDG-PET/CT result in course of follow-up examinations.