Optimistic Bias and Personality Factors in Adherence to Oral Anticancer Treatments in Metastatic Breast Cancer: A Retrospective Analysis of Data From a Randomized Controlled Trial

Introduction: Patients with cancer may overestimate their ability to adhere to oral anticancer treatments (OAT) which may significantly reduce adherence rates. However, only few studies have investigated the specific role of personality traits and cognitive distortions in the definition of the adherence trajectory in the cancer field. Methods: This study is nested in the Pfizer project (65080791), and it is a secondary, observational analysis of prospectively collected data from a randomized controlled trial (RCT). To avoid potential bias from comparing measurements across different time points, we limited the evaluation of associations among variables to the baseline data. 94 metastatic breast cancer (MBC) patients (mean age 56.8) receiving OAT for MBC have been enrolled. Each participant filled a set of measures assessing personality (Big Five), adherence (AAI-28 and MMAS-8) (© 2006 Donald E Morisky), and optimistic bias (VAS), and Quality of Life (EORTC QLQ-C30 and EORTC QLQ-BR23). Results: A discrepancy between self-oriented and other-oriented evaluation of the capacity to take the therapy in the doses, frequencies, and times prescribed was observed (P < 0.001). A negative association between adherence rate and the self-perception of treatment adherence was identified (P < 0.001). Further, conscientiousness correlated positively with the perception of risk to their own health (P = 0.034), and negative association between extraversion and self-perception of treatment adherence (P = 0.05) and between agreeableness and self-perception of treatment adherence have been observed (P = 0.029). Conclusions: Our findings suggest that optimistic bias and personality may contribute to shaping adherence in MBC patients. Personality traits influence adherence both directly, by increasing the perception of health risks, and indirectly, by influencing coping strategies and emotion regulation. MBC patients having an OB may underestimate the important side effects and physical comorbidities, as well as difficulties in the daily management and adjustment of therapy due to disease progression.