Abstract P6-10-06: The impact of body mass index on age at breast cancer diagnosis and breast cancer phenotype
Authors: Brouckaert O , Poppe A , Laenen A , Floris G , Leunen K , Berteloot P , Amant F , Vergote I , Smeets A , Weltens C , Peeters S , Van Limbergen E , Wildiers H , Christiaens M-R , Neven P 
Published: May 2016

Abstract
Background
Evidence suggests that premenopausal obesity decreases and postmenopausal obesity increases breast cancer risk. While it has been hypothesized that carcinogenesis may be accelerated by a disrupted metabolic homeostasis in obese women, it is unclear why this dual relationship is observed. We here study whether body mass index (BMI) affects (a) age at breast cancer diagnosis and (b) the probability of being diagnosed with a specific breast cancer phenotype, taking menopausal status into account.
Patients and methods
All patients with non-metastatic operable breast cancer from UZ Leuven diagnosed between January 1, 2000 and December 31, 2013 were included (n=7020). Luminal A like (= grade 1 or 2, ER and/or PR positive, HER2 negative), Luminal B like (= grade 3 ER and/or PR positive, HER2 negative), Luminal HER2 like (ER and/or PR positive, HER2 positive), HER2 like (ER and PR negative, HER2 positive) and triple negative breast cancer (TNBC = ER and PR and HER2 negative). For statistical analysis, linear models and logistic regression were used to study respectively the association between BMI and age at diagnosis and BMI and breast cancer phenotype by menopausal status.
Results
There was a quadratic relationship between BMI and age at breast cancer diagnosis studying the overall population (p&lt;0.0001). A 5kg/m2 increase in BMI was associated with the following increases in age at diagnosis: +1.8y (95% CI 1.4-2.3y) at BMI=18, +1.2y (95% CI 0.95-1.5y) at BMI=23 and +0.6y (95% CI 0.4-0.9y) at BMI=28 (corrected for menopause). This relationship was independent of the menopausal status, ER or HER2 status, histology and breast cancer phenotype.
We observed a linear relationship between BMI and the probability of being diagnosed with Luminal B like, Luminal HER2 like and HER2 like breast cancer (table 1). This linear relationship interacts with menopausal status for Luminal B like and HER2 like breast cancers (table 1).
Table 1: Probability of being diagnosed with a certain breast cancer phenotype by BMI (linear model) and the impact of menopausal status.Effect of BMI on the probabilityLinear modelof being diagnosed withp-valueeffectLuminal A like0.4430n/aLuminal B like0.0276BMI +5kg/m2 OR 1.07 (95% CI 1.01-1.14)Luminal HER2 like0.0367BMI +5kg/m2 OR 0.91 (95% CI 0.83-1.00)HER2 like0.0219BMI +5kg/m2 OR 0.88 (95% CI 0.78-0.98)TNBC0.5454n/aInteraction with menopausal statusp-valueeffectLuminal A0,2204n/aLuminal B0,0487Premenopausal OR 0,996 (CI 0,974-1,019), p=0,7449; Postmenopausal OR 1,023 (CI 1,008-1,038), p=0.0023Luminal HER20,2571n/aHER2 like0,0031Premenopausal OR 1,020 (CI 0,983-1,059), p=0,2923; Postmenopausal OR 0,947 (CI 0,919-0,976), p=0.0004TNBC0,1638n/a
Conclusion
We could not confirm the hypothesis that increasing BMI decreases (increases) age at diagnosis in postmenopausal (premenopausal) women. Obesity does affect the probability of being diagnosed with certain breast cancer phenotypes, but for certain breast cancer phenotypes an interaction with menopause was observed. We presume a potential biological link through BMI between Luminal B and HER2 like breast cancer that needs further exploration.
Citation Format: Brouckaert O, Poppe A, Laenen A, Floris G, Leunen K, Berteloot P, Amant F, Vergote I, Smeets A, Weltens C, Peeters S, Van Limbergen E, Wildiers H, Christiaens M-R, Neven P. The impact of body mass index on age at breast cancer diagnosis and breast cancer phenotype. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P6-10-06.