Real-world, single-centre prospective data of age at breast cancer onset: Focus on survival and reproductive history

Objectives Being either young or old at the time of breast cancer diagnosis has been suggested as an indicator of a poor prognosis. We studied the effect of age at breast cancer onset in relation to survival, focusing in particular on biological subtypes and reproductive anamnesis. Design, setting and participants Patients with early breast cancer (n=594) treated in a Finnish University Hospital during 2003-2013 were prospectively collected and followed in median 102 months. Results Patients with luminal A-like breast cancer were older than the patients with luminal B-like (HER2-positive) (p=0.045) or patients with the HER2-positive (non-luminal) subtype (p=0.029). Patients ≥70 years received substantially less adjuvant chemotherapy (p=1.5×10-9) and radiotherapy (p=5.9×10-7) than younger women. Nevertheless, the estimated 10-year breast cancer-specific rates of survival were 84.2%, 92.9% and 87.0% in age groups <41 years, 41-69 years and ≥70 years, respectively, with no statistical difference (p=0.115). Survival rates were also comparable between the three age groups when assessed separately in different biological subtypes, and for patients with metastatic breast cancer there was similarly no difference between the age groups. Later menarche (p=5.7×10-8) and high parity (p=0.000078) correlated with increased age at breast cancer diagnosis, but, according to the patients' oestrogen receptor (ER) status, only among ER-positive patients. Conclusions Despite the suggested undertreatment of older patients, we report excellent long-Term outcomes in all age groups in this prospective cohort. Later endogenous endocrine exposure may cause delay in breast cancer onset, but the exact biology behind this phenomenon is so far unclear.