Abstract PO5-09-01: Relative low body mass index (BMI) and fat quantity predicts prognosis better than absolute BMI in hormone receptor-positive, HER2-negative breast cancer

Abstract Purpose: Most existing research about obesity and prognosis in breast cancer patients primarily compares obese and non-obese individuals according to standard body mass index (BMI) categories. With a notably high percentage of Asian patients presenting with young age onset and normal weight, the prevalence of overweight and obesity based on absolute BMI values is lower in Asia (according to WHO guideline, BMI under 18.5 means underweight, and BMI over 25 means overweight). Understanding the impact of relatively low and high weight on prognosis can provide more insightful data than assessments based on absolute BMI thresholds. This study aimed to investigate the impact of relative low/high BMI on the prognosis of breast cancer and to explore the influence of body fat quantity (FQ), which is closely related to BMI. Methods: The study population consisted of 3,663 patients who received surgery for primary breast cancer at Seoul National University Hospital from 2006 to 2015. Pre-treatment BMI was divided into quartiles, defining low-BMI (Q1) as ≤ 21.33, high-BMI (Q4) as > 25.53, and mid-BMI as values between the two. Fat quantity (FQ) was derived from chest CT using the deep learning-based FDA-approved DeepCatch software. It measures the fat volume at the L1 level then divides this value by the square of the patient's height. It was then also divided into quartiles, establishing the definitions of low-, mid-, and high-FQ. The associations of BMI and FQ with distant metastasis-free survival (DMFS) and overall survival (OS) were examined. Results: The high-BMI group demonstrated older median age and higher T and N stages (p< 0.001). The high- and low-BMI groups also showed a higher prevalence of estrogen receptor positive cancer compared to the mid-BMI group. A strong correlation (Pearson correlation coefficient 0.83) was observed between BMI and FQ. In HR-positive, HER2-negative breast cancer, high-BMI patients had a 1.55 times higher risk of distant metastasis (95% CI: 1.15-2.11, p = 0.005), and a 1.78 times higher risk of mortality (95% CI: 1.22-2.58, p = 0.003) compared to mid-BMI patients, while low-BMI patients demonstrated better outcomes regarding DMFS (HR 0.67, p=0.035) and OS (HR 0.59, p=0.04). Comparison of FQ with prognosis revealed that the low-FQ patients exhibited better DMFS (HR 0.59, p=0.005) and OS (HR = 0.44, p=0.002) compared to mid-FQ patients in HR-positive, HER2-negative breast cancer. However, when adjusted for T and N stages, low-BMI patients in the HR-positive, HER2-negative group showed no difference in prognosis from mid-BMI patients but better prognosis compared to high-BMI patients. In contrast, when defined using absolute BMI, underweight patients did not show a difference in DMFS (HR 0.72 vs. normal BMI, p = 0.515) and OS (HR 0.91 vs. normal BMI, p = 0.87) compared to those with normal weight and overweight. The low-FQ group had the best prognosis regarding DMFS (HR 0.66 vs. mid-FQ, p=0.032) and OS (HR 0.50 vs. mid-FQ, p=0.008). Conclusions: Low-BMI is a favorable prognostic factor compared to high-BMI for DMFS and OS in HR-positive, HER2-negative breast cancer. The relative BMI defined according to BMI quartiles was a better prognostic factor than to absolute BMI standards. Investigations with FQ showed similar tendencies, suggesting that low BMI's favorable prognostic influence may be associated with fat. Future investigations should aim to validate these results and delve deeper into the underlying mechanisms. Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Soon Ho Yoon work as chief medical officer in MEDICALIP. This author did not involve data/statistical analysis. Other authors have no competing interest to declare. Citation Format: Eunhye Kang, Ji-Jung Jung, Ik Beom Shin, Hawjeong Lee, Jin Young Byeon, Changjin Lim, Hong-Kyu Kim, Hyeong-Gon Moon, Wonshik Han, Jong-Ho Cheun, Soon Ho Yoon, Han-Byoel Lee. Relative low body mass index (BMI) and fat quantity predicts prognosis better than absolute BMI in hormone receptor-positive, HER2-negative breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-09-01.