Abstract PS5-18: Association of factors of the obesity phenotype with breast cancer recurrence risk measured by oncotype recurrence score and short-term response to neoadjuvant endocrine therapy
Background:Increased body mass index (BMI) and metabolic syndrome are associated with an increased risk of breast cancer recurrence. The mechanism(s) responsible for this increased risk are not known, though multiple mechanisms including resistance to endocrine therapy have been proposed. We sought to determine whether obesity and/or metabolic syndrome were associated with intrinsic tumor risk as determined by the Oncotype recurrence score (RS), or with resistance to neoadjuvant endocrine therapy, as determined by Ki67 response after short-term presurgical treatment. Methods:To investigate whether BMI was associated with increased intrinsic recurrence risk, we analyzed a cohort of 779 patients treated at Vanderbilt for early stage breast cancer and who had Oncotype test results. Medical records were reviewed to record BMI at the time of breast cancer diagnosis. We compared the Oncotype RS between patients with BMI greater or less than 27, and in normal, overweight, and obese ranges. To investigate whether the increase in breast cancer recurrence risk associated with obesity could be identified by a surrogate marker of short-term response to endocrine therapy, we analyzed data from a presurgical trial of endocrine therapy in early stage breast cancer patients previously completed at Vanderbilt. In this study patients were treated with 1-2 weeks of letrozole prior to surgery, then the surgical specimen was analyzed for Ki67. The original goal of the study was to compare endocrine sensitive tumors with endocrine resistant tumors as a platform for discovery of resistance mechanisms to endocrine therapy. We retrospectively analyzed medical records for 143 patients in that study who had post-treatment Ki67 values available, and for whom BMI at the time of surgery could be obtained. We also reviewed medical records for components of the metabolic syndrome (hypertension, hyperglycemia or anti-hyperglycemic medications, low HDL, high triglycerides or statin use, and BMI > 30 as a surrogate for waist circumference). Metabolic syndrome was defined as 3 or more of the 5 components. For endocrine therapy response, a cutoff of 1 for the natural log Ki67 expression was defined as sensitive (approximately 2.5%) and tumors with natural log of Ki67 expression between 1 and 2 (approximately 7.5%) were categorized as intermediate sensitivity. Results:We did not find any significant association between BMI and recurrence score and the distribution of risk scores was similar across all BMI groups. We did not observe any correlation between RS and BMI. However we did observe a difference in the proportion of endocrine sensitive and resistant tumors in overweight and obese groups (only a minority of patients in this cohort, 18%, had normal weight). In patients with overweight, 70% of the tumors had a post-treatment Ki67 level classified as sensitive, whereas only 40% of the tumors in patients with obesity were endocrine sensitive (chi square = 0.0518). Similarly, 72% of patients without metabolic syndrome had sensitive tumors, but only 51% of patients with metabolic syndrome had sensitive tumors (relative risk 1.408, chi square = 0.0154). Conclusions:Our findings suggest that the association between obesity and/or metabolic syndrome and increased recurrence risk is not reflected in tumor-intrinsic properties present at the time of diagnosis. Rather, the effect of obesity and metabolic syndrome appears to be in response to treatment, at least as measured by a short-term surrogate marker of long-term endocrine sensitivity. Importantly, this suggests that interventions to reverse obesity and/or metabolic syndrome may be effective in improving outcomes for breast cancer recurrence, at least in part by improving sensitivity to endocrine therapy. Citation Format: Riley Bergman, Yvonne Berko, Brent Rexer. Association of factors of the obesity phenotype with breast cancer recurrence risk measured by oncotype recurrence score and short-term response to neoadjuvant endocrine therapy [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS5-18.