Low-fat dietary pattern and cancer incidence in the Women's Health Initiative Dietary Modification Randomized Controlled Trial.
BACKGROUND
The Women's Health Initiative Dietary Modification (DM) Randomized Controlled Trial evaluated the effects of a low-fat dietary pattern on chronic disease incidence, with breast cancer and colorectal cancer as primary outcomes. The trial protocol also listed ovarian cancer and endometrial cancer as outcomes that may be favorably affected by the intervention.


METHODS
A total of 48,835 postmenopausal women were randomly assigned during 1993-1998 to a DM intervention (n = 19,541) or comparison (usual diet; n = 29,294) group and followed up for an average of 8.1 years. The intervention goal was to reduce total fat intake to 20% of energy and to increase consumption of vegetables, fruits, and grains. Cancer outcomes were verified by pathology report review. We used weighted log-rank tests to compare incidence of invasive cancers of the ovary and endometrium, total invasive cancer, and invasive cancers at other sites between the groups. All statistical tests were two-sided.


RESULTS
Ovarian cancer risk was lower in the intervention than in the comparison group (P = .03). Although the overall ovarian cancer hazard ratio (HR) was not statistically significantly less than 1.0, the hazard ratio decreased with increasing intervention duration (P(trend) = .01). For the first 4 years, the risk for ovarian cancer was similar in the intervention and control groups (0.52 cases per 1000 person-years in the intervention group versus 0.45 per 1000 person-years in the comparison group; HR = 1.16, 95% confidence interval [CI] = 0.73 to 1.84); over the next 4.1 years, the risk was lower in the intervention group (0.38 cases per 1000 person-years in the intervention group versus 0.64 per 1000 person-years in the comparison group; HR = 0.60, 95% CI = 0.38 to 0.96). Risk of cancer of the endometrium did not differ between the groups (P = .18). The estimated risk of total invasive cancer was slightly lower in the intervention group than in the control group (HR = 0.95, 95% CI = 0.89 to 1.01; P = .10).


CONCLUSIONS
A low-fat dietary pattern may reduce the incidence of ovarian cancer among postmenopausal women.
Prentice
Ross L
RL
Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, PO Box 19024, Seattle, WA 98109-1024, USA. rprentic@fhcrc.org
Thomson
Cynthia A
CA
Caan
Bette
B
Hubbell
F Allan
FA
Anderson
Garnet L
GL
Beresford
Shirley A A
SA
Pettinger
Mary
M
Lane
Dorothy S
DS
Lessin
Lawrence
L
Yasmeen
Shagufta
S
Singh
Baljinder
B
Khandekar
Janardan
J
Shikany
James M
JM
Satterfield
Suzanne
S
Chlebowski
Rowan T
RT
D000368:Aged; D018269:Carcinoma, Endometrioid / Q000453:epidemiology / Q000517:prevention & control; D018284:Cystadenocarcinoma, Serous / Q000453:epidemiology / Q000517:prevention & control; D004041:Dietary Fats / Q000008:administration & dosage*; D002523:Edible Grain; D016889:Endometrial Neoplasms / Q000453:epidemiology* / Q000208:ethnology / Q000473:pathology / Q000517:prevention & control*; D005247:Feeding Behavior; D005260:Female; D005500:Follow-Up Studies; D005638:Fruit; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D009367:Neoplasm Staging; D009369:Neoplasms / Q000453:epidemiology / Q000517:prevention & control; D016017:Odds Ratio; D010051:Ovarian Neoplasms / Q000453:epidemiology* / Q000208:ethnology / Q000473:pathology / Q000517:prevention & control*; D017698:Postmenopause; D016016:Proportional Hazards Models; D018570:Risk Assessment; D012307:Risk Factors; D014481:United States / Q000453:epidemiology; D014675:Vegetables; D015431:Weight Loss; D016387:Women's Health
D004041:Dietary Fats