(see Poster Gallery) Illness Uncertainty and Quality of Life in Patients with Advanced Cancer and Family Caregivers: An Actor-Partner Interdependence Model Analysis

Background and Purpose: Illness uncertainty is defined as “the inability of a person to determine the meaning of illness-related events”. It can persist across the cancer trajectory. Patients’ and caregivers’ individual perceptions of illness uncertainty adversely affect their quality of life (QOL). The relationship between uncertainty and QOL have been examined extensively for either the patient or caregiver, but not among the patient-caregiver dyads. This study aimed to examine the independent and interdependent relationships between illness uncertainty and QOL among patients with advanced cancer and caregivers, and how patient-caregiver relationship (i.e., spouse vs. non-spouse) and type of advanced cancer (i.e., breast, lung, colorectal, and prostate) moderated these relationships.

Methods: This cross-sectional study is a secondary analysis of the baseline data from a randomized clinical trial (N = 484 patient-caregiver dyads). Illness uncertainty and QOL were measured using the Mishel Uncertainty in Illness Scale and the Functional Assessment of Cancer Therapy. The actor–partner interdependence model (APIM) was used to examine whether an individual’s (either a patient or caregiver) illness uncertainty was associated with their own QOL (i.e., an actor effect-independent) and their partner’s QOL (i.e., a partner effect - interdependent). Multigroup structural equation models were used to examine the moderation effects. Patient and caregiver demographic and health-related variables were included in the analyses as covariates.

Results: Significant actor effects were present: patients’ uncertainty was negatively associated with their own QOL (b = -.422; p < .001) and caregivers’ uncertainty was negatively associated with their own QOL (b = -.408; p < .001). In terms of partner effects, patients’ uncertainty was negatively associated with caregivers’ QOL (b = -.095; p < .01). No partner effect was found for caregivers, suggesting that caregivers’ uncertainty was not related to patients’ QOL. The actor and partner effects did not vary by the types of patient-caregiver relationship. The actor and partner effects varied by the type of cancer. Specifically, the caregivers’ actor effect among lung cancer patient-caregiver dyads was significantly larger than that of prostate cancer patient-caregiver dyads (b = -.471 vs. b = -.241, respectively; p < .05). The caregivers’ actor effect among breast cancer patient-caregiver dyads was significantly larger than prostate cancer patient-caregiver dyads (b = -.470 vs. b = -.241, respectively; p < .05). The caregivers’ partner effect among breast cancer patient-caregiver dyads was significantly larger than that among colorectal cancer patient-caregiver dyads (b = -.137 vs. b = .037, respectively; p < .05).

Conclusions and Implications: This study extends previous research by examining the independent and interdependent relationships between illness uncertainty and QOL in patients with advanced cancer and their family caregivers, providing further evidence to support targeted interventions to manage uncertainty and ultimately improve QOL among both patients with advanced cancer and their family caregivers. Our findings also highlighted the importance of viewing patient-caregiver dyad as the unit of care. Understanding different patterns of relationships between illness uncertainty and QOL that exist in patient-caregiver dyads with different backgrounds could facilitate the tailoring of family-focused interventions based on the dyads’ characteristics.