Risk for second primary non-breast cancer in pre- and postmenopausal women with breast cancer not treated with chemotherapy, radiotherapy or endocrine therapy

INTRODUCTION: We investigated the risk for a second primary cancer in pre- and postmenopausal women with breast cancer treated by surgery alone, to assess the importance of non-treatment factors and menopausal status.

PATIENTS AND METHODS: The cohort comprised 14,151 women with breast cancer diagnosed during 1977-2006, who did not receive radiotherapy or systemic adjuvant therapy. They were identified in the nationwide clinical database of the Danish Breast Cancer Cooperative Group. The women were followed for a second primary cancer other than breast cancer in the Danish Cancer Registry, and risk was quantified as standardised incidence ratios (SIRs).

RESULTS: Women with breast cancer diagnosed before menopause had an 18% greater overall risk for a second primary non-breast cancer than the general female population (95% confidence interval [CI], 1.06-1.32). The excess was confined to cancers of the endometrium (1.5; 95% CI, 1.0-2.0) and ovaries (1.8; 95% CI, 1.2-2.4). Rare histological subtypes of breast cancer were associated with these two cancer sites. Women with breast cancer after menopause had no overall excess risk for a second cancer (SIR, 0.98; 95% CI, 0.92-1.04).

CONCLUSION: An excess risk for second non-breast cancers related to non-treatment factors is seen primarily in breast cancer patients who were premenopausal at diagnosis.