Social support as a predictor of deficit accumulation in older breast cancer survivors and non-cancer controls

Introduction: Deficit accumulation is an important construct in oncology, associated with chemotherapy toxicity, cognitive decline, quality of life, and survival. However, longitudinal patterns of deficit accumulation among cancer survivors remain poorly characterized, and the influence of social health on these trajectories is even less understood. We examined long-term deficit accumulation trajectories in older breast cancer survivors compared with non-cancer controls and evaluated the role of social health in predicting these trajectory memberships. Methods: We included 380 breast cancer survivors and 359 frequency-matched controls enrolled from 2010-2022, each with at least three annual follow-ups through 2024. Social health measures included emotional and tangible support using the Medical Outcomes Study Social Support (MOS-SS) tool, social and family well-being using the Functional Assessment of Cancer Therapy-General (FACT-G) subdomain, and social network size (number of close friends/relatives; categorized as >3 vs. ≤3). Deficit accumulation was assessed at each visit using a 46-item index. Group-based trajectory modeling identified distinct deficit accumulation patterns, and multinomial logistic regression examined predictors of trajectory membership. Results: Three trajectories were identified: 204 rapid decliners (28%; 5-year increase 0.06 [0.012/year], p<10 -5 ), 362 slow decliners (49%; 0.005 increase [0.001/year], p=0.3), and 173 non-decliners (23%; 0.005 decrease [-0.001/year], p=0.4). Breast cancer survivors were more likely to follow a rapid-declining trajectory than non-cancer controls. Among survivors, those who received chemotherapy were most likely to experience rapid deficit accumulation, suggesting persistent treatment-related vulnerability. Higher emotional support predicted lower odds of declining trajectories: each 10-point increase in emotional social support was associated with a 14% lower probability of being a slow decliner (aOR 0.86 [0.74-1.01]) and a 23% lower probability of being a rapid decliner (aOR 0.77 [0.65-0.92]). Higher social and family well-being similarly predicted 15% (aOR 0.85 [0.73-0.99]) and 21% (aOR 0.79 [0.68-0.93]) lower odds of being slow and rapid decliners, respectively. Having more than 3 close friends predicted a 65% lower probability of becoming a rapid decliner (aOR 0.38 [0.17-0.87]). Conclusions: Deficit accumulation trajectories in older women are heterogeneous, and breast cancer diagnosis and chemotherapy appear to contribute to more rapid deficit accumulation. Social health-including emotional support, social and family well-being, and larger social networks-emerged as a strong protective factor, slowing the pace of deficit accumulation among both breast cancer survivors and non-cancer controls.