Quality of Life in Adults With Metastatic Breast Cancer: The Impact of Between‐ and Within‐Person Changes in Symptoms and Positive Affect

INTRODUCTION: Quality of life (QoL) is important for patients with metastatic breast cancer (MBC). We examined QoL in daily life among patients with MBC using ecological momentary assessment (EMA). METHODS: From 2023 to 2024, patients with MBC were recruited from 5 Mid-Atlantic sites. Eligible patients were English- or Spanish-speaking, with a life expectancy > 6 months and access to a smartphone. Participants were invited to complete 12 EMAs over 4 weeks. EMAs assessed global QoL, symptom severity (depression, anxiety, pain, fatigue, slowed cognition, appetite loss, nausea, gastrointestinal distress, decreased libido), and positive affect (social connection, peace, joy). Multilevel mixed-effects models analyzed the relationships between QoL and between-person and within-person variations in symptom severity and positive affect. We also explored associations between QoL and years since MBC diagnosis at the time of study entry. RESULTS: Participants (N = 108; Mean age 57.8 years) were a mean of 4.4 years post-diagnosis (range = 0.06-20.65 years). Between-person effects indicated QoL was worse among individuals reporting more nausea (β = -0.109, p = 0.035) and less joy (β = 0.593, p < 0.001). Within-person effects indicated individuals' QoL was lower at times when they had more depression (β = -0.177, p < 0.001), anxiety (β = -0.049, p = 0.023), fatigue (β = -0.052, p = 0.009), appetite loss (β = -0.053, p = 0.028), and decreased libido (β = -0.058, p = 0.036) and less social connectedness (β = 0.091, p = 0.001), joy (β = 0.055, p = 0.047), and peace (β = 0.107, p < 0.001) than their personal average. QoL was not associated with years since MBC diagnosis (β = 0.106, p = 0.956). Age (β = 0.482, p = 0.013) and being partnered (β = 13.356, p = 0.005) at baseline were positively associated with estimated QoL at MBC diagnosis. Changes in QoL per year since MBC diagnosis were positively associated with being employed at baseline (β = 2.453, p < 0.001) and negatively associated with HR positive disease (β = -1.334, p = 0.001). CONCLUSIONS: Both within-person and between-person variations in symptom severity and positive affect are associated with QoL, highlighting the need for adaptive, targeted intervention strategies to optimize QoL for all patients.