Complex organ-system multimorbidity and mortality in long-term breast cancer survivors

Background

Long-term breast cancer survivors tend to have a higher multimorbidity burden than women without cancer, but complexity of this burden and its contribution to mortality risk remain understudied. We aimed to characterize and compare multimorbidity complexity across both groups and examine its association with mortality.

Methods

SURBCAN is a real-world data, multicentric retrospective cohort, including long-term breast cancer survivors from different Spanish regions, paired by age and health area with cancer-free women. Chronic diseases were classified into 13 organ-systems, based on ICD10 codes. No multimorbidity was defined as having less than two chronic diseases, and complex multimorbidity as four or more diseases across four or more organ-systems. Adjusted Cox models with multimorbidity interactions were performed to assess mortality risk.

Results

A total of 18,740 women, 6,269 of which were long-term breast cancer survivors, were followed-up between 2012-2021. Long-term breast cancer survivors had higher mean number of chronic diseases (3.91 vs 3.54), and 18.49% had no multimorbidity compared with 24.33% of women without breast cancer history (p < 0.001). At baseline, complex multimorbidity was higher among long-term breast cancer survivors (40.64% vs 34.10%, p < 0.001). In the adjusted survival models, mild and complex multimorbidity had a higher mortality risk (HR 1.27, 95%CI 1.08-1.48; HR 1.68, 95%CI 1.62-2.20) regardless of breast cancer history. Being a cancer survivor showed a higher mortality risk in women without multimorbidity (HR 1.71, 95%CI 1.28-2.29), and lower for women with mild (HR 1.52, 95%CI 1.32-1.75) and complex multimorbidity (1.35, 95%IC 1.22-1.50).

Conclusions

Multimorbidity complexity, measured as number of organ-systems involved, shapes mortality risk and moderates the effect of breast cancer history. These results support the need of a comprehensive approach to assess chronic disease burden in long-term breast cancer survivors.

Key messages

• Long-term breast cancer survivors have higher organ-system multimorbidity burden, with more diseases across different organs, increasing its complexity.

• The effect of multimorbidity complexity can moderate mortality risk associated with long-term breast cancer survivorship.