The Association Between Survival and Receipt of Post-mastectomy Radiotherapy According to Age at Diagnosis Among Women With Early Invasive Breast Cancer: A Population-Based Cohort Study

• Published in: Clinical oncology (Royal College of Radiologists (Great Britain)) 2023-04, Vol.35 (4), p.e265-e277
• Main Authors: Miller, K., Gannon, M.R., Medina, J., Clements, K., Dodwell, D., Horgan, K., Park, M.H., Cromwell, D.A.
• Format: Article
• Language: English
• Subjects: Aged; Breast cancer; Breast Neoplasms - radiotherapy; Breast Neoplasms - surgery; Cohort Studies; Female; Humans; Mastectomy; Neoplasm Staging; older patient; post-mastectomy radiotherapy; Radiotherapy, Adjuvant; Retrospective Studies; survival
• ISSN: 0936-6555; 1433-2981
• DOI: 10.1016/j.clon.2023.01.008

Clinical trials of post-mastectomy radiotherapy (PMRT) for early invasive breast cancer (EIBC) have included few older women. This study examined whether the association between overall survival or breast cancer-specific survival (BCSS) and receipt of PMRT for EIBC altered with age. The study used patient-level linked cancer registration, routine hospital and radiotherapy data for England and Wales. It included 31 243 women aged ≥50 years diagnosed between 2014 and 2018 with low- (T1-2N0), intermediate- (T3N0/T1-2N1) or high-risk (T1-2N2/T3N1-2) EIBC who received a mastectomy within 12 months from diagnosis. Patterns of survival were analysed using a landmark approach. Associations between overall survival/BCSS and PMRT in each risk group were analysed with flexible parametric survival models, which included patient and tumour factors; whether the association between PMRT and overall survival/BCSS varied by age was assessed using interaction terms. Among 4711 women with high-risk EIBC, 86% had PMRT. Five-year overall survival was 70.5% and BCSS was 79.3%. Receipt of PMRT was associated with improved overall survival [adjusted hazard ratio (aHR) 0.75, 95% confidence interval 0.64–0.87] and BCSS (aHR 0.78, 95% confidence interval 0.65–0.95) compared with women who did not have PMRT; associations did not vary by age (overall survival, P-value for interaction term = 0.141; BCSS, P = 0.077). Among 10 814 women with intermediate-risk EIBC, 59% had PMRT; 5-year overall survival was 78.4% and BCSS was 88.0%. No association was found between overall survival (aHR 1.01, 95% confidence interval 0.92–1.11) or BCSS (aHR 1.16, 95% confidence interval 1.01–1.32) and PMRT. There was statistical evidence of a small change in the association with age for overall survival (P = 0.007), although differences in relative survival were minimal, but not for BCSS (P = 0.362). The association between PMRT and overall survival/BCSS does not appear to be modified by age among women with high- or intermediate-risk EIBC and, thus, treatment recommendations should not be modified on the basis of age alone. •Assessed if the association between PMRT and 5-year OS and BCSS changed with age among women aged 50+ years with EIBC.•Women stratified into three groups based on recurrence risk: low (T1-2N0), intermediate (T1-2N1/T3N0) high (T1-2N2/T3N1-2).•PMRT associated with improved survival for women in the high-risk group, but not in the low- or intermediate-risk groups.•Found no evidence that