Étude cas témoin de la nutrition, du style de vie et du cancer du sein chez les femmes Canadiennes Françaises porteuses d’une mutation fondatrice sur un des gènes BRCA 1 ou BRCA 2

Breast cancer is a multifactorial disease and several dietary and lifestyle factors have been implicated in the development of breast cancer.  Women carriers of a BRCA1 or BRCA2 germline mutation have a lifetime risk of 50 to 80% to develop breast cancer compared with 11 % in non carriers.  Several studies have reported the existence of an association between the incidence of sporadic breast cancers, dietary factors and lifestyle which lead us to investigate the effects of these factors on breast cancer risk in women carriers of a BRCA1 or BRCA2 mutation.  We have carried out a case-control study among French Canadian women in Montreal. Cases were from a cohort of around 1000 women affected with breast cancer, recruited since 1994. We have identified 44 affected women who have been tested for BRCA1 and BRCA2 for six founders mutations in the French Canadian population. All these cases were carriers of one of the six mentioned mutations.  Controls were also women carriers of one of these six in BRCA1 or BRCA2 mutations but, unaffected with cancers. Fifteen of them coming from the same families of the studied cases and twenty-nine were identified at the familial cancer clinic of the CHUM, resulting in a total of 44 controls.  A core questionnaire was administered to both cases and controls to gather information on socio-demographic and lifestyle risk factors covering the two years preceding the diagnosis of breast cancer for cases and the two years before the discovery of the mutation for controls.  A validated semi-quantitative food frequency questionnaire was administered to ascertain dietary intake corresponding to the same period of time for both cases and controls.   A positive and significant association between breast cancer risk and higher education was observed among subjects with a universitary education (> 14 years of study) compared with subjects who had no more than high school education (<11 years of studies) [OR = 7.82, 95% CI :( 1.99-30.69), p = 0.003].  We have found that breast cancer risk increased when gene mutation carriers reached their maximum weight at age> 48 years [OR = 4.27; 95% CI (0.82-22.25)].   In this study it was observed that breast cancer risk in carriers decreased with more than 7 months breast feeding compared with no breastfeeding [OR = 0.35, 95% CI = (0.12-1.06)] but this association was not significant.   Women who practiced more than 22.45 MET-hours per week of moderate physical activity, compared with those practicing less than 11.45 MET-hours per week had a cancer risk decreased by 72% [OR = 0,28 - 95% IC (0.08-0.95), p = 0.04]. Those who practiced more than 31.95 MET-hours per week of total physical activity compared with less than 16.40 showed a risk reduced of around 79% [OR = 0.21; 95% CI:(0.06-0.75), p = 0.02].  The analysis of macro and micro-nutrients and food groups showed that consumption of more than 23.20 g/d of monounsaturated fatty acid increased the risk of breast cancer significantly compared with a consumption of less than 17.08 g/d [OR = 6.00, 95% CI:(0.97-37.02), p = 0.05].  We also observed that an intake of more 221.79 mg/d of vitamin K reduced the risk of breast cancer by 83% compared with those consuming less than 143.57 mg/d [OR = 0.17, 95% (0.05-0.61), p = 0.007].  High intake of fruits was associated with a lower risk of breast cancer risk (73%) among carriers who consumed more than 563.31 g / d compared with less than 356.18 g/d [OR = 0.27; 95% CI :(0.07-1.01), p = 0.05].  The results of our study support the role of lifestyle and dietary habits in the aetiology of breast cancer among French Canadian with a BRCA1 or BRCA2 mutation.    In general, we have observed that a high level of educational and weight gain increased the risk of breast cancer among gene mutation carriers, while breastfeeding and a moderate physical activity reduced this risk.  Regarding food habits and nutrition, our results suggest that high intake of mono-unsaturated fatty acids increased the risk of breast cancer. The higher intake of vitamin K and fruits showed a protective role against breast cancer.  In our knowledge, this is the first finding of the possible relationship between nutrition, lifestyle and risk of breast cancer among French Canadian carriers of BRCA1 or BRCA2 mutation. Due to the small sample size of our study, more investigations are needed in the future to clarify this relationship.

Keyphrases: BRCA, Nutrition, Breast cancer, BRCA, French Canadian, Nutrition, Lifestyle