"Just As I Expected": A Longitudinal Cohort Study of the Impact of Response Expectancies on Side Effect Experiences During Radiotherapy for Prostate Cancer.

CONTEXT: Previous research has indicated that pretreatment response expectancies of side effects often predict subsequent toxicity severity. However, this has been largely based on female patients undergoing chemotherapy.

OBJECTIVES: We tested whether this association also occurred in a novel cohort, men with prostate cancer undergoing radiotherapy. We investigated these associations throughout treatment (before and after side effects were medically predicted to occur), controlling known and novel variables.

METHODS: Homogenous male patients scheduled for radiotherapy (N = 35, mean age 71 years) completed baseline (pretreatment) measures; response expectancies of 18 treatment-related side effects; questions about baseline health and hormonal treatment, emotional state, and coping style. Response expectancies of the side effects were again measured two weeks into treatment. The severity of the same 18 toxicities was assessed two and seven weeks into treatment.

RESULTS: Hierarchical multiple linear regressions revealed baseline response expectancies significantly and independently predicted six of 18 toxicities two weeks into radiotherapy, contributing 12%-30% of explained variance (β = 0.39-0.59). Response expectancies assessed two weeks into treatment significantly and uniquely predicted seven of 17 experienced toxicities at seven weeks, explaining 17%-50% of variance (β = 0.49-0.91). Sexual toxicity response expectancies revealed the strongest associations with experience throughout treatment (β = 0.46-0.91), with "inability to reach orgasm" showing the largest effect.

CONCLUSION: In this older male sample, response expectancies of side effects predicted experiences throughout treatment, including the period before toxicities were medically expected. Response expectancies of sexual side effects were robust, independent predictors of subsequent toxicities across treatment, especially issues with orgasm, warranting focus in practice and future research.