Regular consumption of green tea and the risk of breast cancer recurrence: follow-up study from the Hospital-based Epidemiologic Research Program at Aichi Cancer Center (HERPACC), Japan

Abstract

Experimental studies suggest various features of anticancer activity of green tea including inhibitory effect of tumor invasion and metastasis. This study was conducted to examine the association between regular green tea consumption prior to diagnosis and subsequent risk of breast cancer recurrence. The Hospital-based Epidemiologic Research Program at Aichi Cancer Center (HERPACC) was started in 1988, in which information on lifestyle has routinely been collected from all first-visit outpatients by questionnaire. A total of 1160 new surgical cases of female invasive breast cancers with HERPACC information diagnosed between June 1990 and August 1998 were followed up through December 1999, and the risk (hazard ratio: HR) of recurrence was assessed with reference to daily green tea consumption using a Cox proportional hazard model. During 5264 person-years of follow-up, 133 subjects (12%) were documented to suffer recurrence of breast cancer. A decreased HR for recurrence adjusted for stage was observed with consumption of three or more daily cups of green tea (HR=0.69, 95% confidence interval (95%CI)=0.47–1.00). Particularly in stage I, the HR was decreased statistically significantly (HR=0.43, 95%CI=0.22–0.84). A similar tendency was observed for stage II subjects, but was not present among more advanced stages. Although careful interpretation is needed, these results suggest the possibility that regular green tea consumption may be preventive against recurrence of breast cancer in early stage cases.

Introduction

Tea drinking is common worldwide, but with a wide variety of the types. Green tea is widely consumed in Japan, where it is a major beverage. Health benefits have been recognized for years and green tea contains a high level of polyphenol compounds known as catechins [1]. Experimental studies have demonstrated anticancer activity for such components, including inhibitory effects on tumor formation, growth, invasion and metastasis [2], [3], [4], [5]. Green tea has obvious advantages over other anticancer chemicals since it can be consumed at high dose without toxicity [5].

Breast cancer is the most common cancer among females in developed countries [6]. With its incidence in Japanese is low compared with that in these high rate countries, rapid increase has become apparent and the age-adjusted incidence rate of breast cancer overtook that of gastric cancer in females in 1994 [7]. Given the importance of breast cancer prevention and ease of practical application as a preventive measure, epidemiological assessment of the effects of green tea consumption on breast cancer risk in the Japanese population is of obvious importance. Despite the strong experimental evidence of anticancer effects of green tea on breast cancer [5], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], epidemiological data on mammary neoplasia are limited. There has been only one previous epidemiological report focusing on the inhibitory effects of green tea on tumor invasion and metastasis, a lower recurrence rate with high consumption of green tea being observed for early stage cases only [20].

With special reference to the effects of green tea on prognosis, we conducted a follow-up study of Japanese breast cancer cases. The objective was to gain further epidemiological evidence on the association between daily green tea consumption prior to diagnosis and the risk of recurrence among breast cancer cases, on the hypothesis that the association might be the inverse.