A prospective study of long-term intake of dietary isoflavones and lignans on the risk of recurrence and mortality in Chinese women with early-stage breast cancer

  • Topic:
  • Institution: The Chinese University of Hong Kong
  • Country: Hong Kong
  • Status: Ongoing

Scientific abstract

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Background

The effects of dietary phytoestrogens on breast cancer outcomes remain inconclusive. Conflicting results arose from in vitro and vivo studies and epidemiological studies cannot conclude whether dietary phytoestrogens are safe, have null or beneficial effects, to breast cancer survivors. To date, only two studies have concurrently examined both isoflavones and lignans on breast cancer outcomes (11, 28). No data is available in Asia about the effects of both post-diagnosis dietary isoflavone and lignan intakes on endocrine therapies or overall survival.

Hypothesis and Objectives

Hypothesis: Habitual high intake of dietary isoflavones (including soy and other food sources) and lignans is associated with a reduced risk of breast cancer recurrence or mortality among breast cancer survivors.

Objective I: To evaluate the association of pre- and post-diagnosis soy food intake with the risk of breast cancer recurrence, mortality, and all-cause mortality among Chinese women with early-stage breast cancer at 60-m post-diagnosis.

Objective II: To quantify the intake of dietary isoflavones (including soy and other food sources) and lignans at 36-m and 60-m post-diagnosis, and to examine their individual and joint effects on the risk of breast cancer recurrence, mortality, and all-cause mortality among Chinese women with early-stage breast cancer at 60-m post-diagnosis.

Setting and Methods

Setting: A 60-m prospective cohort study built on an existing ongoing 3-y study on the effects of soy intake and breast cancer prognosis in Hong Kong.

Subjects: 1420 Chinese breast cancer survivors recruited between January 2011 and June 2013 at two regional hospitals. Eligibilities are women in the original cohort study who have completed the baseline interviews and are free of recurrence at the time of study invitation. Women are excluded if they are at stage IV cancer or have breast cancer recurrence. A written consent will be obtained.

Methods: An interviewer-based food frequency questionnaire is used to collect information on intake of soy, other isoflavone-rich foods, lignan-rich foods, and overall diet at 36-m and 60-m post-diagnosis. A structured questionnaire is used to collect information on sociodemographics and lifestyles factors. Information on prognostic factors is extracted from pathological reports. Anthropometric data are measured using standardized protocols. Dietary analyses: Dietary intake of isoflavones and lignans will be quantified based on published databases. Energy and nutrient intakes will be quantified based on China Food Composition Table 2002(33).

Statistical analyses: Multivariate Cox proportional hazards regression models will be used to evaluate the associations of quartiles of dietary isoflavones and lignans with the defined outcomes (recurrence, breast cancer mortality and all-cause mortality). Adjustment will be made for the potential confounders and key prognostic predictors. Stratified analyses will be performed by treatment types, hormone receptor status, menopausal status, use of endocrine therapies, and cancer stages.

Impact

With the fast growing population of breast cancer survivors, the study will contribute to the existing limited data on the effects of dietary phytoestrogen on breast cancer outcomes. Data on whether phytoestrogen-rich foods are recommended or avoided are urgently required. The study results will guide both clinicians and breast cancer survivors on the safety of dietary isoflavones or lignans, and dietary recommendations regarding soy and other phytoestrogen-rich foods.


Plain language abstract

Background

The effects of dietary phytoestrogens on breast cancer outcomes remain inconclusive. Conflicting results arose from cell or animal studies and human studies cannot conclude whether dietary phytoestrogens are safe, have no effects, or beneficial, to breast cancer survivors. Only two studies have examined both isoflavones and lignans on breast cancer outcomes (11,28). No data is available in Asia about the effects of both post-diagnosis dietary isoflavone and lignan intakes on hormonal therapies or overall survival.

Aims and Objectives

This study aims to examine whether habitual high intake of dietary isoflavones (including soy and other food sources) and lignans is related to a lower chance of breast cancer recurrence or mortality among breast cancer survivors.

Objective I: To examine the effects of pre- and post-diagnosis soy intake on breast cancer outcomes (recurrence and mortality) among Chinese women with early-stage breast cancer at 60-m after diagnosis.

Objective II: To estimate the intake of dietary isoflavones (including soy and other food sources) and lignans at 36-m and 60-m after diagnosis, and to examine their relation with the chances of breast cancer outcomes (recurrence and mortality) among Chinese women with early-stage breast cancer at 60-m after diagnosis.

How It Will Be Done

Setting: A follow-up study built on an ongoing 3-y study on the effects of soy intake and breast cancer prognosis in Hong Kong.

Subjects: 1420 Chinese breast cancer survivors recruited between January 2011 and June 2013 at two regional hospitals. Women in the original ongoing study are invited for participation if they have completed the initial interviews and are free of recurrence at the time of invitation. Women who are at stage IV cancer or have breast cancer recurrence will not be invited. A written consent will be obtained.

Methods: Face-to-face interviews using a food frequency questionnaire is used to collect information on intakes of soy, other isoflavone-rich foods, lignan-rich foods, and overall diet at 36-m and 60-m after diagnosis. A structured questionnaire is used to collect sociodemographics and lifestyles factors. Disease information is extracted from medical records up to 60-m after cancer diagnosis. Body measurement will be conducted using standard methods.

Dietary analyses: Dietary intake of isoflavones and lignans will be calculated using published databases. Energy and nutrient intakes will be calculated using China Food Composition Table 2002(33).

Statistical analyses: Advance statistical methods for follow-up studies will be used to examine the relationship between high and low intakes of dietary isoflavones and lignans with the defined outcomes (recurrence and mortality). Other factors that may relate to the dietary phytoestrogen intake or breast cancer outcomes will be considered. Analyses will be performed by subgroups (treatment types, hormone receptor status, menopausal status, use of endocrine therapies, and cancer stages).

Potential Impact

With the fast-growing population of breast cancer survivors, the study will add to the limited data on the effects of dietary phytoestrogen on breast cancer outcomes. The results of the study will guide both clinicians and breast cancer survivors on the safety of dietary isoflavones or lignans, and provide dietary recommendations regarding soy and other phytoestrogen-rich foods.