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Int J Cancer. 2019 Aug 12. doi: 10.1002/ijc.32621. [Epub ahead of print]

Progesterone receptor status modifies the association between body mass index and prognosis in women diagnosed with estrogen receptor positive breast cancer.

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Département de médecine sociale et préventive, Faculté de médecine, Université Laval, Quebec City, Qc, Canada.
CHU de Québec-Université Laval Research Center (Oncology division), Université Laval Cancer Research Center, Quebec City, Qc, Canada.
Centre for Research in Epidemiology and Populations Health, INSERM U.1018, Villejuif, France.
Centre des maladies du sein Deschênes-Fabia, CHU de Québec, Quebec City, Canada.


The role of progesterone receptor (PR) status on the association between obesity and prognosis of estrogen receptor positive (ER+) breast cancer (BC) remains poorly understood. We aim to examine whether this association varies according to the tumor PR status. Data for 3747 women diagnosed with non-metastatic ER+ invasive BC between 1995 and 2010 were analyzed. Women were classified according to their body mass index (BMI) (<18.5, 18.5-24.9, 25.0-29.9 or ≥30.0 kg/m2 ). Tumor PR status (PR-, PR+) was evaluated by immunohistochemistry. Hazard ratios (HR) for survival outcomes were estimated using multivariable Cox regression models. Effect modification was assessed on both additive and multiplicative scales using relative excess risk due to interaction (RERI) and ratio of HRs, respectively. After a median follow-up of 5.9 years (range: 3.4-9.2), women with PR- tumors and underweight (HR=2.76, 95%CI: 1.40-4.91), overweight (HR=2.02, 95%CI: 1.43-2.81) or obese (HR=2.51, 95%CI: 1.67-3.65) had increased risk of all-cause mortality, when compared to normal weight women with PR+ tumors. A similar pattern of associations was observed for BC-specific mortality. In contrast, women with PR+ tumors had similar risks for both mortality outcomes, regardless of BMI. On the additive scale, all-cause mortality was modified by PR status for overweight and obese women, whereas for BC-specific mortality, it was only modified for underweight women. The same observations were found on the multiplicative scale. These results suggest that poorer survival associated with low and high BMI among women diagnosed with ER+ BC may depend on the tumor PR status. This article is protected by copyright. All rights reserved.


Breast cancer; effect modification; obesity; progesterone receptor; prognosis


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