Abstract PD12-02: PD12-02 Obesity is associated with poor breast cancer prognosis, particularly among women with low socioeconomic position

Abstract Purpose: To examine the association between obesity and breast cancer outcomes and to describe socioeconomic position (SEP) in patients enrolled in the Malmö Diet and Cancer Study (MDCS) according to anthropometric measures. Patients and methods: The MDCS is a prospective cohort study that enrolled 17,035 female individuals in Malmö, Sweden from 1991 to 1996. The primary objective of the MDCS was to investigate associations between dietary patterns and cancer risk. Body mass index (BMI) and waist circumferences were measured upon enrollment, in the MDCS cohort. We identified all female MDCS participants with incident invasive breast cancer diagnosed between 1991 and 2014. The primary endpoint was breast cancer recurrence, defined as the time from breast cancer diagnosis until the earliest occurrence of invasive loco-regional recurrence or distant metastases. Follow-up time began at breast cancer diagnosis and continued until the first of breast cancer recurrence, death, emigration, or end of follow-up (June 8, 2020). BMI and waist circumference were categorized according to the World Health Organization guidelines as healthy weight (18.5-24.9 kg/m2 or waist < 81 cm), overweight (25.0-29.9 kg/m2 or waist 81-85 cm), and obese (≥ 30.0 kg/m2 or waist > 85 cm). Consistent with the Swedish socioeconomic classification, we categorized labor status into two groups—manual labor and non-manual labor. We categorized socioeconomic position (SEP) as low if patients had unskilled manual labor with < 2 years post-high school education, low-middle if skilled manual labor with > 2 years of post-high school education, high-middle if assistant non-manual labor with < 3 years of post-high school education, and high if non-manual labor with > 3 years of post-high school education. We fit Cox regression models to compute crude and adjusted hazard ratios (HRs) with 95% confidence intervals (95% CI) of breast cancer recurrence as well as all-cause mortality according to BMI and waist circumference. To evaluate effect measure modification, we stratified the Cox models by labor status, SEP, and smoking. Results: Among 1,099 breast cancer patients, 263 breast cancer recurrences were diagnosed over 12,810 person-years with a median follow-up of 11.1 years (interquartile range [IQR] was 6.6-16.2). The cohort consisted of 556 patients with healthy weight, 384 patients with overweight, and 159 patients with obesity. The median age at breast cancer diagnosis was 66.3 years (IQR: 61.2-72.8), and patients with obesity were older than patients with healthy weight (69.2 vs 64.9 years). In multivariable analyses, having obesity according to BMI was associated with increased rate of recurrence (HR= 1.44 [95% CI: 1.00-2.07]) and all-cause mortality (HR= 1.50 [95% CI: 1.13-1.98]) in comparison to having healthy weight. Similarly, having obesity according to waist circumference was associated with higher risk of recurrence (HR= 1.31 [95% CI: 0.98-1.77]) and all-cause mortality (HR= 1.72 [95% CI: 1.39-2.13]) in comparison to having healthy weight. When evaluating effect measure modification, we observed that obesity was associated with breast cancer recurrence in obese non-smoking women (HR= 1.66 [95% CI: 1.01-2.73]), in obese women with manual labor (HR= 2.45 [95% CI: 1.22-4.93]), and obese women with low SEP (HR= 2.55 [95% CI: 1.08-6.02]). We observed little evidence of an association between obesity and breast cancer recurrence among smokers (HR= 1.12 [95% CI: 0.43-2.92]), among patients with non-manual labor (HR= 0.94 [95% CI: 0.44-2.00]), or among patients with high SEP (HR= 1.47 [95% CI: 0.58-3.75]). Conclusion: Obesity defined by pre-diagnostic levels of BMI and waist circumference was associated with an increased risk of recurrence and all-cause mortality among breast cancer patients. The association between obesity and breast cancer recurrence seems dependent on patient characteristics such as labor status, socioeconomic position, and smoking. Citation Format: Sixten Harborg, Maria Feldt, Deirdre Cronin-Fenton, Susanne Dalton, Ann Rosendahl, Signe Borgquist. PD12-02 Obesity is associated with poor breast cancer prognosis, particularly among women with low socioeconomic position [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD12-02.