Abstract CT043: Low-fat dietary pattern and breast cancer mortality in the Women's Health Initiative (WHI) randomized trial
Authors: Chlebowski Rowan T. , Aragaki Aaron K. , Anderson Garnet L. , Thomson Cynthia A. , Manson Joanne E. , Simon Michael S. , Howard Barbara V. , Rohan Thomas E. , Snetselaar Linda , Lane Dorothy , Barrington Wendy E. , Vitolilns Mara Z. , Womack Catherine , Qi LiHong , Hou Lifang , Thomas Fridtjof , Prentice Ross L. 
Published: July 2016

Context: The Women's Health Initiative Dietary Modification trial randomized 48,835 postmenopausal women at 40 US clinical centers from 1993 to 1998. With 1,767 incident breast cancers, during 8.3 years (mean) dietary intervention, there were fewer breast cancers in the dietary group (HR 0.92 95% CI 0.84-1.01, P = 0.09) with somewhat fewer deaths from breast cancer (HR 0.77 95% CI 0.48-1.22), but no apparent post-intervention influence (JAMA 2006; 295:629; Cancer Epi Bio Prev 2014; 23:2924). These findings suggested dietary intervention may reduce breast cancers associated with greater mortality. New information on breast cancer mortality is analyzed here.

Objective: To examine low-fat dietary pattern influence on breast cancer mortality for cases diagnosed during the dietary intervention period.

Design and Setting: Secondary analyses from a randomized controlled dietary modification trial.

Participants: 48,835 postmenopausal women, 50 to 79 years old, with no previous breast or colorectal cancer, with dietary fat intake greater than 32% of total energy and with a mammogram not suspicious for cancer at entry.

Interventions: Dietary group (40%, n = 19,541) which included nutritionist led group sessions throughout the 8.3 year (mean) dietary intervention. Usual diet control group participants received diet-related education materials (60%, n = 29,294).

Main Outcome Measures: Deaths from breast cancer (breast cancer followed by deaths directly attributed to the cancer) and deaths after breast cancer (breast cancer followed by death from any cause) during 8.3 years (mean) dietary intervention including all 48,835 study participants measured from randomization. Secondarily, breast cancer overall survival (survival from diagnosis with death from any cause) for the 1767 breast cancer cases identified during the dietary intervention period and followed through August, 2014.

Results: Baseline demographic characteristics and breast cancer risk factors were closely comparable in the two randomization groups as was screening mammography frequency throughout. In the dietary group, fat intake decreased, vegetable, fruit and grain consumption increased and body weight was modestly reduced (all P &lt;0.001). In the dietary group, deaths from breast cancer were somewhat lower (HR 0.68 95% CI 0.43-1.07, P = 0.09), while deaths after breast cancer were significantly reduced (40 vs 94

cases; HR 0.65 95% CI 0.45-0.94, P = 0.02). Breast cancer overall survival, among the 1,767 breast cancer cases, after 10.9 years (mean) post-diagnosis follow-up, was greater in the dietary group (10 year survival, 82% vs 78%, HR 0.80 95% CI 0.66-0.97, P = 0.02). Temporal trends for dietary modification influence on breast cancer overall survival identified more favorable effect during dietary intervention then post-intervention (interaction P = 0.02). Causes of death (available for 400 of 487 breast cancer cases) included breast cancer (41%, 165 deaths), other cancer (17%, 67 deaths), and cardiovascular disease (16%, 64 deaths, HR 0.45 95% CI 0.25-0.81 for dietary influence).

Conclusion: Compared to a usual diet control group, a low-fat dietary pattern led to a lower incidence of deaths after breast cancer. This reduction is due, in part, to better survival following breast cancer diagnosis.

Citation Format: Rowan T. Chlebowski, Aaron K. Aragaki, Garnet L. Anderson, Cynthia A. Thomson, Joanne E. Manson, Michael S. Simon, Barbara V. Howard, Thomas E. Rohan, Linda Snetselaar, Dorothy Lane, Wendy E. Barrington, Mara Z. Vitolilns, Catherine Womack, LiHong Qi, Lifang Hou, Fridtjof Thomas, Ross L. Prentice. Low-fat dietary pattern and breast cancer mortality in the Women's Health Initiative (WHI) randomized trial. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr CT043.