Interaction between obesity-related genes, FTO and MC4R, associated to an increase of breast cancer risk

Breast cancer (BC) is a complex disease and obesity is a well-known risk factor for its development, especially after menopause. Several studies have shown Single Nucleotide Polymorphisms (SNPs) linked to overweight and obesity, such as: rs1121980 (T/C) and rs9939609 (A/T) in Fat Mass and Obesity Associated gene (FTO) and rs17782313 (T/C) in Melanocortin 4 Receptor gene (MC4R). Thus, we aimed to investigate the association between these obesity-related SNPs and BC risk. One hundred BC patients and 148 healthy women from Santa Catarina, Brazil entered the study. SNPs were genotyped using Taqman assays. For statistical analyses SNPStats and SPSS softwares were used. Association analyses were performed by logistic regression and were adjusted for age and Body mass index (BMI). Multiple SNPs inheritance models (log-additive, dominant, recessive, codominant) were performed to determine odds ratios (ORs), assuming 95 % confidence interval (CI) and P value = 0.05 as the significance limit. When analyzed alone, FTO rs1121980 and rs9939609 did not show significant associations with BC development, however MC4R rs17782313 showed increased risk for BC even after adjustments (P-value = 0.032). Interestingly, the interaction of FTO and MC4R polymorphisms showed a powerful association with BC. We observed a 4.59-fold increased risk for woman who have the allele combination C/T/C (FTO rs1121980/FTO rs9939609/MC4R rs17782313) (P-value = 0.0011, adjusted for age and BMI). We found important and unpublished associations between these obesity-related genes and BC risk. These associations seem to be independent of their effect on BMI, indicating a direct role of the interaction between FTO and MC4R polymorphisms in BC development.