Background Rebound thymic hyperplasia (RTH) is a common phenomenon caused by stress factors such as chemo- (CTX) or radiotherapy with an incidence of up to 40%. Misinterpretation of RTH and thymic lymphoma relapse (LR) may lead to unnecessary diagnostic procedures including invasive biopsies or treatment intensification. The aim of this study was to identify parameters that differentiate between RTH and thymic LR in the anterior mediastinum. Methods After completion of CTX, we analyzed CTs and MRIs of 291 patients with classical Hodgkin lymphoma (CHL) and adequate imaging available from the European Network for Pediatric Hodgkin lymphoma C1-trial. In all patients with biopsy proven LR an additional FDG-PET-CT was assessed. Structure and morphologic configuration in addition to calcifications and presence of multiple masses in the thymic region and signs of extrathymic LR were evaluated. Results After CTX, a significant volume increase of a new or growing mass in the thymic space occurred in 133 of 291 patients. Without biopsy only 100 patients could be identified as RTH or LR. No single finding related to thymic regrowth allowed differentiation between RTH and LR. However, the vast majority of cases with thymic LR presented with additional increasing tumor masses (34/35). All RTH patients (65/65) presented with isolated thymic growth. Conclusion Isolated thymic LR is very uncommon. CHL relapse should be suspected when increasing tumor masses are present in distant sites outside of the thymic area. Conversely, if regrowth of lymphoma in other sites can be excluded, an isolated thymic mass after CTX likely represents RTH.

Background: Since the beginning of SARS-CoV-2 pandemic, it has been widely recognized that children and adolescents seem to have milder clinical courses as compared to adult counterparts. However, there is concern that vulnerable collectives including pediatric patients treated for cancer or under immunosuppression may be at higher risk. Methods: We retrospectively collected Spanish COVID-19 cases in children and adolescents with solid and hematological malignancies, non-malignant chronic hematologic conditions, and post allogeneic-stem cell transplantation, from the beginning of the pandemic on January 31 to April 24, 2020. Results: We included 47 cases with RT-PCR positive COVID-19 from 41 centers in Spain, where 97.6% of pediatric patients are treated for cancer. In most cases (76.6%), infection was asymptomatic, or symptoms were mild. Severe illness was observed in 14.9% of cases with respiratory distress and/or hypoxemia, and 8.5% required admission to the PICU. Symptomatic patients received supportive care associated with antiviral and immunomodulatory agents depending upon severity. Anticancer therapy was withhold in the majority of cases during the infection course. Most patients recovered from COVID-19. Two deaths were reported. Conclusion: In our cohort, most children receiving anticancer chemotherapy presented a mild clinical course and had a good outcome. Highly immunosuppressed patients with major comorbidities were at higher risk of severe infections. Among this fragile collective, individualized expert discussion is critical for anti-infectious therapy and appropriate anticancer treatment.