Etiology and risk factors of febrile neutropenia in children during cancer treatment

Abstract: Side effects due to chemotherapy is still a major issue during cancer treatment. Febrile neutropenia and associated microbiological defined infections (MDIs) are dreaded complications, and still a cause of death during pediatric cancer treatment. In many of the febrile neutropenia episodes the cause of the fever is unknown, and risk factors of developing febrile neutropenia are poorly characterized. To be able to pin-point children at risk of febrile neutropenia and anticipate those at risk of more severe episodes could lead to more individualized treatment. Therefore, the aim of this thesis was two-fold: to investigate the microbiological causes of febrile neutropenia episodes and to investigate risk factors of developing this condition and associated MDIs. In papers I and IV, causes of febrile neutropenia episodes were assessed. In paper I, we identified a respiratory virus in 45% of the episodes, which was in line with earlier reports. In addition, followup nasopharyngeal sampling showed that only rhinovirus and coronavirus were persistent and all other viruses cleared from the nasal cavity. This indicated that the respiratory virus identified was indeed the cause of the fever. However, causality could not be established. Therefore, paper IV investigated the innate immune response during these episodes. By using gene-expression profiling, the aim was to investigate specific innate signatures in blood. Unfortunately, due to the immunosuppression, there was insufficient RNA from ~30% of the samples and a specific innate signature, similar to that of immunocompetent children, could not be identified. Therefore, the feasibility of using geneexpression profiling to correlate the microbiological findings to an active infection and as a diagnostic tool in children treated for cancer remains challenging. In papers II and III, risk factors of developing neutropenia and febrile neutropenia with associated MDI and low end doses of 6-Mercaptopurine (6-MP) during pediatric ALL treatment were addressed. In paper II, genetic variants in important enzymes involved in drug metabolism were investigated. Here, TPMT genetic variants were associated with a decreased risk of developing neutropenia and febrile neutropenia during the maintenance II period, and deficiency in ITPA (rs1127345) to a decreased risk of developing febrile neutropenia (unadjusted). In addition, genetic variants in NUDT15 were associated with decreased end doses of 6-MP. From the results from paper II, we could still not fully understand the role of TPMT and ITPA and the risk of febrile neutropenia. In addition, NUDT15 seem to play an important role for the 6-MP doses. However, due to the small samples sizes, our results need further investigation in larger cohorts. In paper III, the febrile neutropenia episodes were characterized and genetic variants in important innate immune proteins were investigated. Viral infections were the most common detected infection during febrile neutropenia episodes. However, in the majority of the episodes the cause of the fever remained unknown. TLR4 genetic variants increased the risk of viral infections and variants in the IL-1Ra gene decreased the risk of developing bacterial bloodstream infection. There were no association between MBL and the investigated genetic variants. Therefore, TLR4 and IL-1Ra seem to have a role during infectious episodes in children treated for cancer, however, the results needs to be confirmed in future studies. In conclusion, respiratory virus are common during febrile neutropenia. However, additional more sensitive methods are needed to be able to identify and prove causality between the microbiological findings and the febrile neutropenia episode. Some of the investigated genetic variants seem to play a role in the risk of developing febrile neutropenia and infections. However, some of these need to be further evaluated before any modifications of the management of febrile neutropenia could be recommended.