Multimorbidity clusters among long-term breast cancer survivors in Spain: Results of the SURBCAN Study.

The disease management of long-term breast cancer survivors (BCS) is hampered by the scarce knowledge of multimorbidity patterns. The aim of this study was to identify multimorbidity clusters among long-term BCS and assess their impact on mortality and health services use. We conducted a retrospective study using electronic health records of 6512 BCS from Spain surviving at least 5 years. Hierarchical cluster analysis was used to identify groups of similar patients based on their chronic diagnoses, which were assessed using the Clinical Classifications software. As a result, multimorbidity clusters were obtained, clinically defined, and named according to the comorbidities with higher observed/expected prevalence ratios. Multivariable Cox and negative binomial regression models were fitted to estimate overall mortality risk and probability of contacting health services according to the clusters identified. 83.7% of BCS presented multimorbidity, essential hypertension (34.5%) and obesity and other metabolic disorders (27.4%) being the most prevalent chronic diseases at the beginning of follow-up. Five multimorbidity clusters were identified: C1-Unspecific (29.9%), C2-Metabolic and neurodegenerative (28.3%), C3-Anxiety and fractures (9.7%), C4-Musculoskeletal and cardiovascular (9.6%), and C5-Thyroid disorders (5.3%). All clusters except C5-Thyroid disorders were associated with higher mortality compared with BCS without comorbidities. The risk of mortality in C4 was increased by 64% (adjusted Hazard Ratio 1.64, 95%CI 1.52-2.07). Stratified analysis showed an increased risk of death among BCS with 5-10 years of survival in all clusters. These results help to identify sub-groups of long-term BCS with specific needs and mortality risks and to guide BCS clinical practice regarding multimorbidity. This article is protected by copyright. All rights reserved.