Clinical and psychological moderators of the effect of mindfulness-based cognitive therapy on persistent pain in women treated for primary breast cancer - explorative analyses from a randomized controlled trial.
Mindfulness-based intervention has been found efficacious in reducing persistent pain in women treated for breast cancer. Little, however, is known about possible moderators of the effect. We explored clinical and psychological moderators of the effect on pain intensity previously found in a randomized controlled trial of mindfulness-based cognitive therapy (MBCT) with women treated for breast cancer with persistent pain. A total of 129 women treated for breast cancer reporting persistent pain were randomized to MBCT or a wait-list control. The primary outcome of pain intensity (11-point numeric rating scale) was measured at baseline, post-intervention, three, and six months follow-up. Proposed clinical moderators included age, axillary lymph node dissection (ALND), radiotherapy, and endocrine treatment. Psychological moderators included psychological distress [the Hospital Anxiety and Depression Scale (HADS)], the adult attachment dimensions anxiety and avoidance [the Experiences in Close Relationships Short Form (the ECR-SF)], and alexithymia [the Toronto Alexithymia Scale (TAS-20)]. Multi-level models were used to test moderation effects over time, i.e. time × group × moderator. Only attachment avoidance (p = 0.03, d = 0.36) emerged as a statistically significant moderator. Higher levels of attachment avoidance predicted a larger effect of MBCT in reducing pain intensity compared with lower levels attachment avoidance. None of the remaining psychological or clinical moderators reached statistical significance. However, based on the effect size, radiotherapy (p = 0.075, d = 0.49) was indicated as a possible clinical moderator of the effect, with radiotherapy being associated with a smaller effect of MBCT on pain intensity over time compared with no radiotherapy. Attachment avoidance, and potentially radiotherapy, may be clinically relevant factors for identifying the patients who may benefit most from MBCT as a pain intervention. Due to the exploratory nature of the analyses, the results should be considered preliminary.