Prognostic Impact of De-escalation Therapy in Older Adults With Breast Cancer: A Retrospective Cohort Study.

Background With global population aging, breast cancer is increasingly diagnosed in older adults, and individuals aged 70 years and above now account for over 30% of new cases. Standard treatments, including surgery, radiation, endocrine therapy, and chemotherapy, are effective in reducing recurrence and improving survival. However, older patients remain underrepresented in clinical trials, resulting in limited evidence specific to this population. In clinical practice, de-escalated adjuvant therapies are often employed in older patients, but their prognostic impact remains uncertain. This study aimed to evaluate recurrence outcomes according to treatment intensity in elderly breast cancer patients. Methods We conducted a retrospective cohort study of 399 breast cancer patients aged ≥70 years who underwent surgery at Kobe City Medical Center General Hospital between July 2011 and March 2023. Patients were classified as receiving either standard or de-escalated adjuvant therapy, with standard therapy defined according to the 2022 Japanese Breast Cancer Clinical Practice Guidelines. Clinical data, including comorbidities, stage, and tumor subtype, were collected. Recurrence-free survival (RFS) was assessed using Cox proportional hazards models, adjusting for clinical covariates. Multiple imputation was performed to address missing data. Subgroup analyses were conducted by age, stage, estrogen receptor (ER) status, and human epidermal growth factor receptor 2 (HER2) status. Results The cohort included 399 patients (median age: 75 years) with a median follow-up of 56 months (interquartile range: 27-89). Only five recurrences (1.3%) were observed. In the unadjusted analysis, the median RFS was 46 months in the standard treatment group and 62 months in the de-escalation group. After adjustment with multiple imputation, the median RFS was not reached in either group. The hazard ratio for recurrence in the standard versus de-escalation group was 0.094 in the unadjusted analysis and 1.51 after adjustment. Notable differences were observed between groups with respect to comorbidities, disease stage, and tumor subtype. Conclusions De-escalated adjuvant therapy may be an appropriate option for selected elderly breast cancer patients, particularly those with favorable disease profiles. The very low recurrence rate observed in this cohort supports individualized treatment strategies that balance efficacy with tolerability. Prospective studies are warranted to confirm these findings and to inform evidence-based decision-making in geriatric oncology.