PET with 18F-Fluorodeoxyglucose/Computed Tomography in the Management of Pediatric Sarcoma

The role for PET with fludeoxyglucose F 18 (¹⁸F-FDG PET)/computed tomography (CT) in the management of pediatric sarcomas continues to be controversial. The literature supports a role for PET/CT in the staging and surveillance of certain specific pediatric sarcoma subtypes; however, the data are less clear regarding whether PET/CT can be used as a biomarker for prognostication. Despite the interest in using this imaging modality in the management of pediatric sarcomas, most studies are limited by retrospective design and small sample size. Additional data are necessary to fully understand how best to use ¹⁸F-FDG PET/CT in pediatric sarcoma management.

Advances in the Diagnosis and Management of Neonatal Sarcomas

Neonatal sarcomas comprise a heterogeneous group of rare soft tissue neoplasms that present unique diagnostic and therapeutic challenges. Recent advances in molecular profiling have improved diagnostic capabilities and reveal novel therapeutic targets. Clinical trials demonstrate differences in behavior between sarcoma subtypes that allow for better clinical management. Surgical resection has been replaced with a multimodal approach that includes chemotherapy and radiotherapy. Despite these advances, neonates with sarcoma continue to fare worse than histologically similar sarcomas in older children, likely reflecting differences in tumor biology and the complexities of neonatal medicine. This review focuses on recent advances in managing neonatal sarcomas.

Efficacy and Safety of Limited-Margin Conformal Radiation Therapy for Pediatric Rhabdomyosarcoma: Long-Term Results of a Phase 2 Study

PURPOSE

Our purpose was to assess disease outcomes and late toxicities in pediatric patients with rhabdomyosarcoma treated with conformal photon radiation therapy (RT).

METHODS AND MATERIALS

Sixty-eight patients (median age, 6.9 years) were treated with conformal photon RT to the primary site on a prospective clinical trial. Target volumes included a 1-cm expansion encompassing microscopic disease. Prescribed doses were 36 Gy to this target volume and 50.4 Gy to gross residual disease. Chemotherapy consisted of vincristine/dactinomycin (n = 6), vincristine/dactinomycin/cyclophosphamide (n = 37), or vincristine/dactinomycin/cyclophosphamide-based combinations (n = 25). Patients were evaluated with primary-site magnetic resonance imaging, whole-body [¹⁸F]fluorodeoxyglucose positron emission tomography, and chest computed tomography for 5 years after treatment.

RESULTS

Five-year disease-free survival was 88% for low-risk (n = 8), 76% for intermediate-risk (n = 37), and 36% for high-risk (n = 23) patients (P ≤ .01 for low risk/intermediate risk vs high risk). The cumulative incidence of local failure (LF) at 5 years for the entire cohort was 10.4%. Tumor size at diagnosis was a significant predictor of LF (P < .01). Patients with head and neck primary tumors (n = 31) had a 35% cumulative incidence of cataracts; the risk correlated with lens dose (P = .0025). Jaw dysfunction was more severe when the pterygoid and masseter muscles received a mean dose of >20 Gy (P = .013). Orbital hypoplasia developed more frequently after a mean bony orbit dose of >30 Gy (P = .041). Late toxicity in patients with genitourinary tumors included microscopic hematuria (9 of 14), bladder-wall thickening (10 of 14), and vaginal stenosis (2 of 5).

CONCLUSIONS

Long-term LF rates were low, and higher rates correlated with larger tumors. Treatment-related toxicities resulting in measurable functional deficits were not infrequent, despite the conformal RT approach.

Assessment of circulating tumor DNA in pediatric solid tumors: The promise of liquid biopsies

Circulating tumor DNA can be detected in the blood and body fluids of patients using ultrasensitive technologies, which have the potential to improve cancer diagnosis, risk stratification, noninvasive tumor profiling, and tracking of treatment response and disease recurrence. As we begin to apply "liquid biopsy" strategies in children with cancer, it is important to tailor our efforts to the unique genomic features of these tumors and address the technical and logistical challenges of integrating biomarker testing. This article reviews the literature demonstrating the feasibility of applying liquid biopsy to pediatric solid malignancies and suggests new directions for future studies.

18F-FDG Uptake During Early Adjuvant Chemotherapy Predicts Histologic Response in Pediatric and Young Adult Patients with Osteosarcoma

The purpose of this study was to determine the relationship of ¹⁸F-FDG uptake in the primary tumor at diagnosis, during therapy, and after therapy with a histologic response and event-free survival in pediatric and young adult patients with osteosarcoma (OS). Methods: Serial (baseline and 5 and 10 wk after start of therapy) ¹⁸F-FDG PET/CT imaging was performed in patients with newly diagnosed OS treated uniformly in a therapeutic trial at a single institution. Whole-body images were obtained approximately 1 h after injection of ¹⁸F-FDG. Logistic regression was used to study the association of tumor uptake and changes in SUV_max between 0, 5, and 10 wk for both clinical endpoints. Results: Thirty-four patients (17 males; median age, 12.2 y; age range, 6.8-19.1 y) underwent PET imaging; 25 (74%) had localized disease. Primary tumor locations included the femur (n = 17; 50%), tibia (n = 9; 26%), and humerus (n = 5; 15%). Logistic regression showed that SUV_max at 5 wk (P = 0.034) and 10 wk (P = 0.022) and percentage change from baseline at 10 wk (P = 0.021) were highly predictive of a histologic response. Using SUV_max of 4.04 at week 5, SUV_max of 3.15 at week 10, and 60% decrease from baseline at week 10 as cutoff values, we determined that the respective sensitivities were 0.93, 0.93, and 0.79 and that the respective specificities were 0.53, 0.71, and 0.76. Conclusion: SUV_max on routine images at 5 or 10 wk and percentage change in SUV_max from baseline to week 10 were metabolic predictors of a histologic response in OS. These findings may be useful in the early identification of patients who are responding poorly to therapy and may benefit from a change in treatment.

The Role of 18F-FDG-PET/CT in Pediatric Sarcoma

Considerable debate remains regarding how best to incorporate ¹⁸F-FDG-PET/CT into clinical practice for pediatric sarcomas. Although there is a clear role for ¹⁸F-FDG-PET/CT in staging pediatric sarcoma, the value of ¹⁸F-FDG-PET/CT in prognostication for pediatric sarcomas remains unclear. In osteosarcoma, Ewing sarcoma, and rhabdomyosarcoma, ¹⁸F-FDG-PET/CT may be most useful in the identification of skeletal metastases, where the literature consistently suggests that it has improved sensitivity and specificity as compared to bone scintigraphy. The role of the imaging modality in the identification of pulmonary metastatic disease is less clear. Further controversy exists regarding the use of ¹⁸F-FDG-PET/CT in predicting outcome. Several studies, particularly in osteosarcoma, suggest changes in the maximal standardized uptake value (SUV_max) that can predict histologic response following neoadjuvant chemotherapy as well as overall outcome. Conversely, studies are conflicting regarding the use of ¹⁸F-FDG-PET/CT as a prognostic tool in Ewing sarcoma and rhabdomyosarcoma. The role of ¹⁸F-FDG-PET/CT in pediatric nonrhabdomyosarcoma soft tissue sarcomas is unknown at this time. Although most studies have been small and retrospective, in certain histologic subtypes, there is a clear role for the use of this imaging modality. Additional prospective and larger studies are needed to fully determine how best to incorporate ¹⁸F-FDG-PET/CT into treatment regimens for pediatric sarcomas in the future.