Prospective study of soy intake and breast cancer prognosis in Chinese breast cancer survivors

  • Topic: Breast cancer
  • Institution: University of Hong Kong
  • Country: Hong Kong
  • Status: Ongoing

Scientific abstract

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Background

Epidemiological studies, particularly those conducted among Asian populations where soy food consumption is common, have generally shown a protective effect of soy food intake on breast cancer risk. However, the relationship between soy intake and survival after breast cancer diagnosis remains uncertain, and breast cancer survivors have been exposed to conflicting recommendations with regard to soy food intake or supplementation. So far, limited data on soy food intake prior to breast cancer diagnosis have shown either beneficial or no adverse effect on breast cancer survival; available data on the association between postdiagnose soy food intake and breast cancer survival also remain inconclusive.

Objective

The objective of the present study is to investigate the effects of habitual soy food intake before and after breast cancer diagnosis on breast cancer prognosis and survival among breast cancer survivors.

Settings and Methods

A prospective study will be conducted in Hong Kong. Chinese women aged 25 to 70 years with incident, primary, histologically confirmed breast cancer will be recruited from two Regional Cancer Treatment Centers (N. T. East and Kowloon West) of Hong Kong and then prospectively followed up for an initial period of 3 years. Face-to-face interviews based on the standardized structured questionnaire will also be conducted to collect information on socio-demographic, menstrual and reproductive factors, menopausal status, use of complementary and alternative medicine, active and passive smoking, drinking and physical activity. Soy food intake and general diet during the year prior to diagnosis will be collected using validated soy food frequency questionnaire and food frequency questionnaire. Interviews on assessment of soy food/supplement intake and other covariates will be repeated at 18-month and 36-month.

The potential clinical covariates will be extracted from medical records and pathology reports. Information on primary breast cancer outcomes including recurrence, breast cancer-specific mortality, all-cause mortality will be obtained from active follow-up, medical records and computerized clinical management system. An initial 3-year followup period is planned but a longer followup period will be conducted with future additional funding. Cox proportional hazards regression models will be carried out to evaluate the associations of soy food intake assessed both before and after diagnosis and the defined outcomes with adjustments for important prognostic predictors and other diet and lifestyle factors.

Impact

Patients diagnosed with cancer are highly motivated to seek information about diet, physical activity, dietary supplement use, and nutritional complementary therapies. Soy foods have generated considerable interest among breast cancer survivors as a complementary or supplementary food for promoting health, but there is great concern on whether the continued habitual soy or additional soy intake will have an adverse effect on recurrence or survival. Our study will add to the limited available data on the association between soy food intake before and after breast cancer diagnosis and breast cancer prognosis. The study results will help provide clinicians and breast cancer survivors with evidence-based recommendations on safety and benefits or harm of soy intake for breast cancer survivors.

Plain language abstract

Background

Soy is a major source of isoflavones, which have structural and functional similarities to human estrogens. Although human studies have not revealed any adverse effects of soy intake on the risk for breast cancer, some in vitro and animal studies have shown that isoflavones promote the proliferation of breast cancer cells. So far, limited data on soy food intake prior to breast cancer diagnosis have shown either beneficial or no adverse effect on breast cancer survival. Two recent publications have shown a suggested reduction of breast cancer recurrence and total mortality among breast cancer survivors with higher postdiagnose soy intake. There is still a lack of data on whether continued or increased soy food intake after breast cancer diagnosis affects breast cancer prognosis. Thus whether breast cancer survivors should continue with habitual or reduce soy intake is of great concern and studies in this area are urgently required.

Aims and goals

This study aims to investigate the effects of habitual soy food intake before and after breast cancer diagnosis on breast cancer prognosis and survival among breast cancer survivors.How it will be done: The study will be conducted in Hong Kong Chinese women aged 25 to 70 years diagnosed with primary breast cancer. The patients will be recruited from two Regional Cancer Treatment Centers (N. T. East and Kowloon West) of Hong Kong and then prospectively followed up for 3 years. Face-to-face interviews based on the standardized structured questionnaire will be conducted to collect information on soy food intake and general diet during the year prior to diagnosis. Information on socio-demographic factors, medical and reproductive history, use of complementary and alternative therapy, menopausal status, active and passive smoking, drinking and physical activity will also be collected. The interviews will be repeated at 18-month and 36-month.  Assessment of soy and overall dietary intake postdiagnosis will be included in the follow-up interviews.  The clinical predictors of breast cancer prognosis will be extracted from the medical records, pathology reports and computerized Clinical Management System (CMS). Information on breast cancer outcomes including recurrence, breast cancer-specific mortality and all-cause mortality will be obtained from active follow-up, medical records, CMS and Department of Health. Analyses will be carried out to evaluate the associations of soy food intake assessed both before and after diagnosis and the defined outcomes with adjustments for known important prognostic predictors and other diet and lifestyle factors.

Potential impact

There is much concern among breast cancer survivors on whether continued habitual or additional intake of soy food will have an adverse effect on breast cancer recurrence or survival. Data on safety of soy food consumption for breast cancer survivors are urgently required. Our study will add to the limited available data on the association between soy food intake before and after breast cancer diagnosis and breast cancer prognosis. The results of the study will help clinicians to provide breast cancer survivors with evidence-based dietary recommendations. The results will also contribute to guiding soy food consumption for breast cancer survivors.