Longitudinal biological exposure to carotenoids is associated with breast cancer-free survival in the Women's Healthy Eating and Living Study

Abstract

In some cohort studies, a high-vegetable diet has been associated with greater likelihood of recurrence-free survival in women diagnosed with breast cancer. Carotenoids are obtained primarily from vegetables and fruit and they exhibit biological activities that may specifically reduce the progression of mammary carcinogenesis. The present analysis examines the relationship between plasma carotenoids at enrollment and 1, 2 or 3, 4, and 6 years and breast cancer-free survival in the Women's Healthy Eating and Living Study participants (N = 3,043), who had been diagnosed with early-stage breast cancer. The primary end point was time to a second breast cancer event (a recurrence or new primary breast cancer). An average carotenoid concentration over time was estimated for each participant as the average area under the plasma carotenoid curve formed by the plasma carotenoid concentrations at scheduled clinic visits. Multiple regression Cox proportional hazards analysis with adjustment for prognostic and other factors was used to examine the association between carotenoids and breast cancer-free survival. A total of 508 (16.7%) breast cancer events occurred over a median 7.12 years follow-up. Compared with the lowest tertile, the hazard ratio for the medium/high plasma carotenoid tertiles was 0.67 (95% confidence interval, 0.54-0.83) after adjustment. The interaction between the study group and tertile of average carotenoid concentration over time was not significant (P = 0.23). Higher biological exposure to carotenoids, when assessed over the time frame of the study, was associated with greater likelihood of breast cancer-free survival regardless of study group assignment.

Figure 1

Percentage of participants in the two study groups who changed across the tertiles during the course of the study.

Figure 2

Kaplan-Meier estimates of breast cancer-free survival by tertile of average plasma carotenoid concentration over time. Average carotenoid concentration over time was estimated as the area under the plasma carotenoid curve (AUC), computed by summing the areas of trapezoids formed by plasma carotenoid concentrations at regularly scheduled clinic visits (described as AUC/yr).