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.