Abstract P6-08-02: The body mass index interacts with the prognostic effect of the progesterone receptor in patients with a luminal HER2 negative breast cancer
Authors: Van Asten Kathleen , Lintermans Anneleen , Laenen Annouschka , Remmerie Chantal , Poppe An , Floris Giuseppe , Wildiers Hans , Christiaens Marie-Rose , Neven Patrick 
Published: May 2015

Abstract
Background
Obesity (body mass index (BMI) &gt;30) increases breast cancer (BC) risk and promotes BC metastases probably through high estrogen levels. A high BMI as a risk and prognostic factor is consistently reported in postmenopausal women. Obese women develop particularly hormone receptor positive, HER2 negative BC. In this study, we investigate the influence of BMI on the prognostic effect of the progesterone receptor (PR) in postmenopausal patients with estrogen receptor (ER) positive, HER2 negative BC.
Patients and methods
Women over 50 years of age diagnosed with primary operable BC between 2000 and 2012 at University Hospitals Leuven were retrieved from the database. Patients were subdivided into normal weight (&lt;25 kg/m2), overweight (&gt;25 and ≤30) and obese (&gt;30). We investigated for each BMI category the distant metastasis free interval (DMFI) and BC specific survival (BCSS) by PR status. Apart from the total cohort, subgroup analysis was performed for luminal A (grade 1-2) and luminal B HER2 negative BC (grade 3). We used Fine and Gray’s competing risk regression for the analyses. Covariates were age at diagnosis, tumor size, lymph node status, and therapy.
Results
In total, 3227 patients were analyzed for DMFI. For BCSS, 3192 patients were analyzed as patients with unknown cause of death were excluded from the analysis. 2395 of all patients had luminal A and 832 had luminal B HER2 negative BC (Table 1). Median time of follow-up was 6.5 years.
Table 1: Percentage of luminal A and luminal B patients per BMI category BMI&lt;25BMI &gt;25 and ≤30BMI &gt;30Luminal A1105 (76%)820 (75%)470 (70%)Luminal B355 (24%)278 (25%)199 (30%)BMI: body mass index
BMI interacts with the prognostic effect of PR for DMFI and BCSS in luminal HER2 negative BCs. Only patients with BMI &lt;25 had a reduction in the risk of distant metastasis and BC-related death if the tumor was PR positive as compared to patients with PR negative BC. This was observed in the total cohort and only seen in the luminal B subgroup (table 2). A similar effect was observed in obese patients but this did not reach statistical significance, and was mainly present during the first 5 years following diagnosis. For the overweight patients, no difference in DMFI and BCSS was observed by PR status.
Table 2: Multivariate analysis for DMFI and BCSS for PR positive versus PR negative in the 3 BMI categories in the total and the luminal B cohort. DMFI (HR, 95% CI)BCSS (HR, 95% CI)Total cohort BMI &lt;250.25, 0.16 to 0.400.22, 0.12 to 0.40BMI &gt;25 and ≤301.24, 0.59 to 2.600.95, 0.40 to 2.25BMI &gt;300.70, 0.33 to 1.490.53, 0.21 to 1.33luminal B BMI &lt;250.19, 0.11 to 0.330.14, 0.06 to 0.31BMI &gt;25 and ≤301.23, 0.44 to 3.481.02, 0.36 to 2.85BMI &gt;300.82, 0.31 to 2.200.61, 0.18 to 2.00BCSS: breast cancer specific survival, BMI: body mass index, CI: confidence interval, DMFI: distant metastasis free interval, HR: hazard ratio
Conclusion
Normal weight patients have a reduced risk of developing distant metastases and of BC-related death if the tumor is PR positive compared to PR negative BC. No difference between PR positive and PR negative cases was observed in overweight BC patients. This BMI-dependent prognostic effect of PR was limited to luminal B BC patients.
Citation Format: Kathleen Van Asten, Anneleen Lintermans, Annouschka Laenen, Chantal Remmerie, An Poppe, Giuseppe Floris, Hans Wildiers, Marie-Rose Christiaens, Patrick Neven. The body mass index interacts with the prognostic effect of the progesterone receptor in patients with a luminal HER2 negative breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P6-08-02.