Adherence to treatment guidelines and survival in patients with early-stage breast cancer by age at diagnosis.

BACKGROUND: Elderly patients with breast cancer are under-represented in clinical studies. It is not known whether treatment guidelines, based on clinical trials, can be extrapolated to this population. The aim of this study was to assess adherence to treatment guidelines by age at diagnosis, and to examine age-specific survival in relation to adherence to guidelines.
METHODS: Patients with early-stage breast cancer aged either less than 65 years, or 75 years or more, diagnosed between 2005 and 2008, were identified from the Netherlands Cancer Registry. Adherence to treatment guidelines for breast and axillary surgery, radiotherapy, chemotherapy and endocrine therapy was determined. Non-adherence to the guidelines was defined as overtreatment or undertreatment. The primary endpoint was overall survival, assessed by means of an instrumental variable, the comprehensive cancer centre region.
RESULTS: Some 24 959 patients younger than 65 years and 6561 patients aged 75 years or more were included in the analysis. Median follow-up was 2·8 years. Compared with patients younger than 65 years, those aged at least 75 years were less frequently treated in concordance with guidelines: 62·0 per cent (15 487 patients) versus 55·6 per cent (3647 patients) (P < 0·001). In both age groups, most patients received at least three of five treatment modalities in concordance with guidelines: 98·8 per cent (24 652 patients) and 93·8 per cent (6152 patients) respectively. Analysis of survival using the instrumental variable showed that adherence to guidelines was not associated with overall survival in patients younger than 65 years (P = 0·601) or those aged at least 75 years (P = 0·190).
CONCLUSION: Adherence to treatment guidelines was affected by age at diagnosis. However, adherence to the guidelines was not associated with overall survival in either age group.