Adherence to the World Cancer Research Fund/American Institute for Cancer Research cancer prevention recommendations and risk of in situ breast cancer in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort
Authors: Karavasiloglou Nena , Hüsing Anika , Masala Giovanna , van Gils Carla H. , Turzanski Fortner Renée , Chang-Claude Jenny , Huybrechts Inge , Weiderpass Elisabete , Gunter Marc , Arveux Patrick , Fournier Agnès , Kvaskoff Marina , Tjønneland Anne , Kyrø Cecilie , Dahm Christina C. , Vistisen Helene Tilma , Bakker Marije F. , Sánchez Maria-Jose , Chirlaque López María Dolores , Santiuste Carmen , Ardanaz Eva , Menéndez Virginia , Agudo Antonio , Trichopoulou Antonia , Karakatsani Anna , La Vecchia Carlo , Peppa Eleni , Palli Domenico , Agnoli Claudia , Panico Salvatore , Tumino Rosario , Sacerdote Carlotta , Butt Salma Tunå , Borgquist Signe , Skeie Guri , Schulze Matthias , Key Timothy , Khaw Kay-Tee , Tsilidis Kostantinos K. , Ellingjord-Dale Merete , Riboli Elio , Kaaks Rudolf , Dossus Laure , Rohrmann Sabine , Kühn Tilman 
Published: December 2019

Abstract
Background
Even though in situ breast cancer (BCIS) accounts for a large proportion of the breast cancers diagnosed, few studies have investigated potential risk factors for BCIS. Their results suggest that some established risk factors for invasive breast cancer have a similar impact on BCIS risk, but large population-based studies on lifestyle factors and BCIS risk are lacking. Thus, we investigated the association between lifestyle and BCIS risk within the European Prospective Investigation into Cancer and Nutrition cohort.

Methods
Lifestyle was operationalized by a score reflecting the adherence to the World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) cancer prevention recommendations. The recommendations utilized in these analyses were the ones pertinent to healthy body weight, physical activity, consumption of plant-based foods, energy-dense foods, red and processed meat, and sugary drinks and alcohol, as well as the recommendation on breastfeeding. Cox proportional hazards regression was used to assess the association between lifestyle score and BCIS risk. The results were presented as hazard ratios (HR) and corresponding 95% confidence intervals (CI).

Results
After an overall median follow-up time of 14.9 years, 1277 BCIS cases were diagnosed. Greater adherence to the WCRF/AICR cancer prevention recommendations was not associated with BCIS risk (HR = 0.98, 95% CI 0.93–1.03; per one unit of increase; multivariable model). An inverse association between the lifestyle score and BCIS risk was observed in study centers, where participants were recruited mainly via mammographic screening and attended additional screening throughout follow-up (HR = 0.85, 95% CI 0.73–0.99), but not in the remaining ones (HR = 0.99, 95% CI 0.94–1.05).

Conclusions
While we did not observe an overall association between lifestyle and BCIS risk, our results indicate that lifestyle is associated with BCIS risk among women recruited via screening programs and with regular screening participation. This suggests that a true inverse association between lifestyle habits and BCIS risk in the overall cohort may have been masked by a lack of information on screening attendance. The potential inverse association between lifestyle and BCIS risk in our analyses is consistent with the inverse associations between lifestyle scores and breast cancer risk reported from previous studies.