Effect of Smoking on Endocrine Therapy for Stage IV Hormone Receptor Positive Breast Cancer

Background: Smoking worsens breast cancer prognosis. It has been reported that tobacco components directly reach mammary gland tissue, causing smoking-related DNA damage and biological effects. We hypothesized that smoking may have a characteristic course other than the therapeutic effect in patients with stage IV hormone receptor-positive breast cancer (HRBC) who received endocrine therapy as the first-line treatment.Methods: Fifty-six patients diagnosed with stage IV HRBC were treated with endocrine therapy as the first-line treatment. Before treatment, the period and amount of smoking were confirmed through patient interviews, and each pack-year was recorded.Results: It was significantly more frequent for smokers to be evaluated for disease progression due to the appearance of new metastases during endocrine therapy as first-line treatment (p=0.034). Furthermore, as the pack-year increased, new metastases tended to appear (pack-year ≤15; hazard ratio [HR] 1.929, p=0.507; pack-year 15–30, HR 3.857, p=0.223; pack-year >30, HR: 7.714, p=0.028).Conclusions: In stage IV HRBC, smoking increases the metastatic potential of breast cancer, suggesting that changes in its biology may lead to poor prognosis.