Age exerts a continuous effect in the outcomes of Asian breast cancer patients treated with breast‐conserving therapy

Background Asians are diagnosed with breast cancer at a younger age than Caucasians are. We studied the effect of age on locoregional recurrence and the survival of Asian breast cancer patients treated with breast‐conserving therapy. Methods Medical records of 2492 patients treated with breast‐conserving therapy between 1989 and 2012 were reviewed. The Kaplan–Meier method was used to estimate locoregional recurrence, breast cancer‐free survival, and breast cancer‐specific survival rates. These rates were then compared using log‐rank tests. Outcomes and age were modeled by Cox proportional hazards. Fractional polynomials were then used to test for non‐linear relationships between age and outcomes. Results Patients ≤ 40 years old were more likely to have locoregional recurrence than were older patients (Hazard ratio [HR] = 2.32, P < 0.001). Locoregional recurrence rates decreased year‐on‐year by 4% for patients with luminal‐type breast cancers, compared with 8% for those with triple‐negative cancers. Similarly, breast cancer‐free survival rates increased year‐on‐year by 4% versus 8% for luminal‐type and triple‐negative cancers, respectively. Breast cancer‐specific survival rates increased with age by 5% year‐on‐year. Both breast cancer‐free survival and breast cancer‐specific survival rates in patients with luminal cancers exhibited a non‐linear (“L‐shaped”) relationship—where decreasing age at presentation was associated with escalating risks of relapse and death. The influence of age on overall survival was confounded by competing non‐cancer deaths in older women, resulting in a “U‐shaped” relationship. Conclusions Young Asian breast cancer patients have a continuous year‐on‐year increase in rates of disease relapse and cancer deaths compared with older patients with no apparent threshold.