Role of PET/CT in malignant pediatric lymphoma.

INTRODUCTION: Malignant pediatric lymphoma accounts for 10-15% of all pediatric cancers, (representing 2-3% of all malignancies), with a peak incidence between 5-9 years. Chemotherapy is usually the first and most common mode of treatment. The choice of treatment and prediction of prognosis depend on the histological type of tumor, initial staging, evaluating treatment response, and detection of early recurrence. Conventional imaging modalities have many limitations. PET/CT is more accurate, however so far the literature lacks the results of a large group of patients. AIM OF STUDY: To report the role of PET/CT in the above-mentioned objectives at the newly established Children's Cancer Hospital in Cairo, Egypt, which is one of the busiest dedicated pediatric oncology centers of such purposes in the world. All findings were proven by histopathology, clinically, and by clinical follow-up. PATIENT POPULATION: A total of 152 patients (35 girls and 117 boys) with histologically proven malignant lymphoma (117 HD, 35 NHL) were included in this study. They were divided into four groups. Group I: 41 patients for initial staging. Group II: 51 patients for evaluating early treatment response after two to three cycles of chemotherapy. Group III: 42 patients for evaluating treatment response 4-8 weeks after the end of their treatment. Group IV: 18 patients evaluated for long-term follow-up. Results of PET/CT were compared with the other conventional imaging modalities (CIM). RESULTS: The sensitivity, specificity, accuracy, and positive and negative predictive values of PET/CT and CIM were as follows: In Group I: PET/CT modified staging and treatment in 11 out of 41 cases (26.8%), upstaged 5(12.2%) patients and down-staged six (14.6%) patients. Group II: 100%, 97.7%, 98%, 85.7%, 100%, respectively, for PET/CT and 83%, 66.6%, 68.6%, 25%, 96.7% for CIM respectively Group III: At the end of chemotherapy 100%, 90.9%, 92.8%, 75%, 100%, respectively, for PET/CT and 55.5%, 57.5%, 57.1%, 26.3%, 82.6% for CIM, respectively. Group IV: For long-term follow-up, all the parameters scored 100% for PET/CT, 100%, 38.4%, 72.2%, 50%, 100% for CIM, respectively. CONCLUSION: PET/CT in pediatric lymphoma is more accurate than CIM. We recommend that it should be the first modality for all purposes in initial staging, evaluating treatment response and follow-up.

False-positive F-18 FDG uptake in PET/CT studies in pediatric patients with abdominal Burkitt's lymphoma.

INTRODUCTION: In pediatric patients with abdominal Burkitt's lymphoma, the involvement of the gastrointestinal tract and abdominal lymph nodes are the main presenting feature of the disease. Chemotherapy is the main treatment modality and could be preceded by surgical excision of the abdominal masses. To achieve cure or long-term disease-free survival a balance has to be struck between aggressive chemotherapy and the probability of tumor necrosis secondary to treatment complicated by acute infections, perforation or intestinal bleeding. F-18 fluorodeoxyglucose-positron emission tomography/computed tomography (F-18 FDG-PET/CT) has been recommended over conventional imaging modalities for the follow-up of these patients and for monitoring treatment response. As the incidences of postchemotherapy complications are high, the positive predictive value of PET/CT studies in these patients is very low and the false-positive rate is high from acute infections and tumor necrosis. Accordingly, histopathological confirmation of positive lesions on F-18 FDG-PET/CT studies is essential. This is especially important as post-therapy complications might present with nonspecific and nonurgent symptoms. At the same time initiating a second course of salvage chemotherapy is risky. AIM OF STUDY: Retrospectively reviewed F-18 FDG-PET/CT studies for 28 pediatric patients with abdominal Burkitt's lymphoma and diffuse large B-cell lymphoma after their treatment with chemotherapy or surgery. RESULTS: Four positive studies were found. All had pathological verification and were because of acute inflammation and tumor necrosis and there was no evidence of viable tumor cells. One patient had multiple recurrent lesions in the abdomen after the initial surgical excision and before starting chemotherapy. The incidence of acute complications in this series is 10.7%. CONCLUSION: This study confirms the high incidence of tumor necrosis and inflammation after chemotherapy for the abdominal Burkitt's lymphoma and consequently, the incidence of true-positive F-18 FDG studies is low. This necessitates the need for histopathological confirmation of positive studies.

Role of 131-I MIBG Therapy in the Treatment of Advanced Neuroblastoma.

INTRODUCTION: Neuroblastoma, a neoplasm of the sympathetic nervous system, is the second most extracranial malignant solid tumor of childhood. Many therapeutic strategies has evolved over the last 20 years, based upon work by international cooperative groups and smaller cohort studies. Novel therapies to improve initial disease response and treatment of minimal residual disease are required to improve survival for these children with highrisk neuroblastoma. Radio-labeled MIBG therapy has been tried in the treatment of advanced stage 3&4 neuroblastoma in an attempt to improve patients' outcome. The use of radio-labeled MIBG to treat neuroblastoma has arisen from the high sensitivity and specificity of in-vivo MIBG imaging for detection of primary and metastatic tumors. AIM OF WORK: To determine the impact of MIBG therapy on neuroblastoma patients' outcome and its impact on their quality of life. PATIENTS AND METHODS: Thirty pediatric patients with stage 4 pathologically proven neuroblastoma are included in this study. Eighteen of the study patients (60%) were males and 12 (40%) were females. All the patients had partially responsive tumor to first-line therapy +/- surgey. 131-I MIBG doses ranged from 100 to 150mCi with number of courses ranged from 1-7 according to response and toxicity. RESULTS: Two patients achieved complete remission (CR) and were still disease-free after 64 &69 months. Nine patients showed partial remission (PR) to 131-I MIBG, all the nine patients were alive at 16-57 months (mean 30.6 months) among whom seven were alive with stable disease and two patients were alive with progressive disease (PD) at the end of study. Eighteen patients remained stable after 131-I MIBG therapy, among them six were alive with PD and four were alive with stable disease at the end of study, while the remaining eight patients died. The last patient developed PD and died within 15 months. The 5 years event free survival (EFS) was 48.2% and the overall survival (OS) was 69%. CONCLUSIONS: We concluded that 131-I MIBG therapy has favorable therapeutic effect for advanced neuroblastoma patients. Controlled clinical trials should be considered to evaluate the true potential of 131-I MIBG therapy. KEY WORDS: MIBG therapy - Advanced neuroblastoma.