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

Smoking worsens breast cancer prognosis. It has been reported that tobacco components directly reach the mammary gland tissue, causing smoking-related DNA damage and biological effects. We hypothesized that smoking may have characteristics that affect the therapeutic effect and clinical course in patients with stage IV hormone receptor-positive breast cancer (HRBC) who received endocrine therapy as the first-line treatment.

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.

Disease progression with new metastases was more frequent in smokers than non-smokers 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].

In stage IV HRBC, smoking increases the metastatic potential of breast cancer, suggesting that changes in its biology may lead to poor prognosis.