Objective: Whether obesity contributes to breast cancer recurrence and breast cancer mortality (BCM) remains uncertain. We investigated the association between moderate–severe obesity (BMI 30 to < 40 kg⁄m2) at diagnosis, and the combined outcome of breast cancer recurrence or BCM, in women with HR+, HER2– disease, taking into account age, tumour characteristics and treatment.
Design: The Bupa Health Foundation Health and Wellbeing after Breast Cancer Study is a prospective cohort study of 1684 women recruited within 12 months of their diagnosis of invasive breast cancer, June 2004 to December 2006, and followed for 5 years. This analysis included 1155 women, mean age, 58.4±11.6 years, with hormone receptor positive (HR+, HER2– ) disease.
Results: 53.8% of the women had Stage–1 disease and 88.9% commenced oral adjuvant endocrine therapy (OAET) within 2 years of diagnosis. Moderate–severe obesity made a significant independent contribution to the likelihood of breast cancer recurrence or BCM (HR = 1.71, 95%CI, 1.12-2.62, p= 0.014).
The other factors independently associated with recurrence or BCM included disease beyond Stage–1 (HR = 2.87, 95% CI 1.73- 4.75, p<0.001), OAET (HR = 0.26, 95% CI 0.14-0.46, p<0.001), mastectomy (HR = 3.28, 95%CI 1.98-5.44, p<0.001) and radiotherapy (HR = 2.12, 95% CI 1.24-3.63, p<0.006). For Stage–1 disease, moderate to severe obesity (HR 3.23, 95% CI 1.48-7.03, p=0.003) and OAET (HR 0.41, 95%CI 0.17-0.98, p<0.046) were significantly independently associated with recurrence or BCM.
Conclusion: Moderate–severe obesity is associated with a poorer prognosis for women with HR+, HER2– disease; this also holds for women with Stage–1 disease, and is independent of age and treatment. As moderate–severe obesity persisted in this analysis, even when controlling for OAET use, our findings support the hypothesis that obesity-associated insulin resistance and /or other factors produced in fat underpin the link between obesity and a poorer breast cancer prognosis.