The role of response expectancies in cancer treatment

Abstract

Cancer incidence continues to grow gradually yet mortality rates have decreased, warranting research on methods of predicting and reducing treatment-related toxicities. This research project explored the influence of response expectancies, individuals’ expectations of their automatic reactions to stimuli (i.e., cancer treatment), on side effect experiences. Although research has supported associations between response expectancies of cancer treatment-related toxicities and subsequent experience, outcomes have not been consistent. Furthermore, whether response expectancies are equally influential in under-investigated patient groups is unknown, and exploration into patients’ side effect reduction through response expectancy-based interventions is still in its infancy. The current project addressed these gaps through a meta-analysis and three empirical studies. Meta-analysis aims (Study 1) were threefold; to replicate the relationship between expectancies of cancer toxicities and subsequent experiences, to explore if association strength differed between individual toxicity expectancies, and to investigate methodology differences on outcomes. In a pooled analysis of 27 quantitative studies, results revealed a moderate relationship between expectancies of all measured side effects and their experience. Further analyses revealed significant differences between individual toxicities, with expectancies of hair loss demonstrating the strongest relationship with subsequent experience. Measurement and sample differences were associated with varying levels of effects, explored more comprehensively using a psychometric design (Study 2). In Study 2, the inclusion of a midpoint representing patients being ‘unsure’ whether they would experience a toxicity, and differences between the two most commonly used scales (5-point and visual analogue scales; VAS), were investigated. Forty-five men scheduled for radiotherapy for prostate cancer completed measures of side effect expectancies on both 5-point scales and VAS. Analyses revealed patients often selected ‘unsure’ on the 5-point scale, which appeared a less sensitive measure of response expectancies than VAS. For most toxicities, responses on the two scales were not highly related. Based on Study 1 and 2, careful consideration is essential when designing and pooling studies. Study 3 collected longitudinal data from the same homogenous sample of patients with prostate cancer (N = 35, Study 2). This prospective study found that baseline response expectancies significantly and uniquely predicted 6 of the 18 radiotherapy toxicities 2-weeks into treatment (where toxicities are not yet medically expected). This signified the influence of response expectancies early in radiotherapy. Seven-weeks into treatment, response expectancies (measured at 2-weeks) predicted 7 of the 16 experienced side effects. Expectancies of sexual toxicities demonstrated moderate-to-strong associations with experience, throughout, and thus should be a clinical and research focus in the future. Study 4 explored whether pre-treatment side effect information presented in different valence frames could influence response expectancy formation and subsequent experience. A healthy sample of 134 university students was randomised to receive information about an experimental pain induction task framed in a positive or negative format. Results revealed that although response expectancies consistently and independently predicted subsequent experience, framing had minimal impact on response expectancies and experience. Social influences through media and social media channels, were found to impact participants’ pain experiences, suggesting a clear direction for future research.