Discussion
This study showed several notable results that support the role of hippocampal volume as a potential biomarker of PTSS severity and intervention response.
First, smaller hippocampal volumes were associated with more severe symptomatology at baseline, which is consistent with prior studies in adults [13,14]. In cancer patients and survivors, smaller hippocampal volume has been reported in adults [23] and children [24], suggesting sensitivity of the hippocampus to the neurotoxic effects of stress and cancer treatment [6,25].
Second, youth with smaller hippocampal volumes at baseline demonstrated greater reductions in cancer-related PTSS following a brief four-week MAT. Congruent with a recent meta-analysis, effects were specific to the left hippocampus, indicating that left hippocampal volume is more closely related to PTSS severity than the right [14]. We found hippocampal volume predicted reductions in re-experiencing and negative affect PTSS subtypes. Re-experiencing PTSS are particularly prevalent in both adult and pediatric cancer populations [6]. Prior research in breast cancer survivors linked greater re-experiencing PTSS to smaller hippocampal volumes [26]. Together, hippocampal volumes may serve not only as a promising biomarker of symptom severity, but also as a predictor of response to psychosocial interventions.
However, neither overall PTSS nor PTSS subtypes showed significant change over the four-week intervention. This may be due to small sample size, heterogeneity in cancer diagnoses, treatments, or age. It is also possible that four weeks was not a sufficient duration to assess change, as mindfulness-based interventions are typically eight weeks in length [27]. Future studies might benefit from a longer intervention period as well as a larger sample size to better assess the effects of MAT on PTSS.
Results of this preliminary study suggest that smaller hippocampal volume may be a predictor of more severe cancer-related PTSS and greater response to a four-week MAT in pediatric cancer populations. This extends prior research on effects of MAT and mindfulness-based practices on mental health in youth. Further, the findings contribute to a new understanding of the neural underpinnings of cancer-related PTSS in youth and highlight potential biomarkers that can be used to guide interventions.