Abstract P2-11-11: Impact of baseline body mass index (BMI) and weight changes after diagnosis in young women with early breast cancer (BC): A multicenter retrospective study
Authors: Franzoi Maria Alice , Punie Kevin , Laenen Annouschka , Dullens Boudewijn , Costa Celia Fernandes , Neven Patrick , Wildiers Hans , Lambertini Matteo , de Azambuja Evandro 
Published: March 2022

Background: Prior studies demonstrated that premenopausal obese women with BC have a poorer prognosis than non-obese patients (pts). We examined time trends in the prevalence of overweight and obesity among young women diagnosed with early BC and assessed the impact of baseline BMI and weight changes in disease outcomes. Patients and methods: Multicenter retrospective cohort study including young women (≤40yrs) diagnosed with stage I-III BC during 2000-2016 treated in two large Belgian hospitals. Data on baseline characteristics, treatment, and survival outcomes were collected. Pts were classified according to baseline BMI into underweight (&lt;18.5 kg/m2), normal weight (18.5-24.9 kg/m2), overweight (25-29.9 kg/m2) and obese (≥30 kg/m2). Landmark analysis at 2y after diagnosis (+/-6 months) was performed to evaluate the impact of weight changes (≥5% from baseline) on disease outcomes. Univariate hazard ratios were calculated for outcomes of interest (invasive disease-free survival [IDFS], distant recurrence-free interval [DRFI], overall survival [OS]). Multivariable analysis adjusting for factors that differed between groups was performed for the analysis of 2 BMI categories. Results: A total of 1,849 eligible pts were included, of whom 1,371 (74.1%) had a BMI recorded: 84 (6.1%) were underweight, 871 (63.5%) had normal weight, 304 (22.1%) were overweight and 112 (8.1%) were obese. Baseline BMI was similar across age groups. Overweight and obese pts had significantly larger tumor size when compared to underweight and normal weight pts (p=0.002) with similar rates of nodal involvement. The proportion of pts diagnosed with a BMI ≥25 significantly increased over time (OR: 1.03; 1.00-1.05 p=0.024). There was no difference in OS, DRFI and IDFS according to baseline BMI when grouping pts in the 4 BMI categories (underweight vs. normal weight vs. overweight vs. obese) or in the 2 BMI categories (underweight/normal weight vs. overweight/obese). Multivariate analysis with 2 BMI categories also did not demonstrate differences in OS, DRFI and IDFS. 1,023 pts had weight registered at 2y follow-up, of whom 360 (35.1%) were overweight, and 107 (10.4%) obese. Regarding weight changes, 117 (11.4%) presented weight loss, 617 (60.4%) stable weight, and 287 (28.1%) had weight gain. Weight gain was significantly associated with the use of endocrine therapy in general (p=0.029) and ovarian function suppression (p&lt;0.001). In pts with baseline BMI ≥25, 59 (18.5%) lost weight, 185 (58%) maintained a stable weight, and 74 (23.2%) continued to gain weight. There was no statistically significant impact of weight changes at 2y on disease outcomes. Conclusions: Our time trend analysis suggests that the prevalence of overweight and obesity among young women with BC is increasing over time, highlighting the need for preventing overweight/obesity. In this retrospective analysis, BMI had no impact on disease outcomes. Prospective studies and analyzes of body composition can add important information in this regard. Weight gain after BC diagnosis was significantly associated with the use of endocrine therapy and ovarian function suppression and is a prevalent issue among young women, with 23% of overweight/obese pts at diagnosis continuing to gain weight. Further studies evaluating weight changes and interventions to prevent weight gain are needed to better inform survivorship programs.

Table 1.- Impact of Baseline BMI and weight changes on disease outcomesOverall survival (OS)4 BMI categories (baseline)Hazard ratio2 BMI categories (baseline)Hazard ratioNormal weightReferenceUnderweight/normal weight (BMI&lt;25)ReferenceUnderweight1.37 (0.8-2.2)Overweight1.01 (0.7-.1.3)Overweight/obese (BMI≥25)1.05 (0.7-1.3)Obese1.28 (0.4-1.2)Distant Recurrence-Free Interval (DRFI)Normal weightReferenceUnderweight/normal weight (BMI&lt;25)ReferenceUnderweight0.86 (0.5-1.3)Overweight0.88 (0.6-1.1)Overweight/obese (BMI≥25)0.91 (0.7-1.1)Obese0.94 (0.6-1.3)Invasive disease-free survival (IDFS)Normal weightReferenceUnderweight/normal weight (BMI&lt;25)ReferenceUnderweight0.88 (0.5-1.3)Overweight0.88 (0.6-1.1)Overweight/obese (BMI≥25)0.92 (0.7-1.1)Obese0.99 (0.6-1.4)Weight changes analysisWeight changes categoryHazard ratio for OSHazard ratio for DRFIHazard ratio for IDFSStable weightReferenceReferenceReferenceWeight Loss1.45 (0.9-2.2)1.11 (0.6-1.8)1.05 (0.6-1.6)Weight Gain0.77 (0.5-1.14)0.92 (0.6-1.3)0.92 (0.6-1.2)

Citation Format: Maria Alice Franzoi, Kevin Punie, Annouschka Laenen, Boudewijn Dullens, Celia Fernandes Costa, Patrick Neven, Hans Wildiers, Matteo Lambertini, Evandro de Azambuja. Impact of baseline body mass index (BMI) and weight changes after diagnosis in young women with early breast cancer (BC): A multicenter retrospective study [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-11-11.