Dairy products and pancreatic cancer risk: a pooled analysis of 14 cohort studies.

Pancreatic cancer has few early symptoms, is usually diagnosed at late stages, and has a high case-fatality rate. Identifying modifiable risk factors is crucial to reducing pancreatic cancer morbidity and mortality. Prior studies have suggested that specific foods and nutrients, such as dairy products and constituents, may play a role in pancreatic carcinogenesis. In this pooled analysis of the primary data from 14 prospective cohort studies, 2212 incident pancreatic cancer cases were identified during follow-up among 862 680 individuals. Adjusting for smoking habits, personal history of diabetes, alcohol intake, body mass index (BMI), and energy intake, multivariable study-specific hazard ratios (MVHR) and 95% confidence intervals (CIs) were calculated using the Cox proportional hazards models and then pooled using a random effects model. There was no association between total milk intake and pancreatic cancer risk (MVHR = 0.98, 95% CI = 0.82-1.18 comparing ≥500 with 1-69.9 g/day). Similarly, intakes of low-fat milk, whole milk, cheese, cottage cheese, yogurt, and ice-cream were not associated with pancreatic cancer risk. No statistically significant association was observed between dietary (MVHR = 0.96, 95% CI = 0.77-1.19) and total calcium (MVHR = 0.89, 95% CI = 0.71-1.12) intake and pancreatic cancer risk overall when comparing intakes ≥1300 with <500 mg/day. In addition, null associations were observed for dietary and total vitamin D intake and pancreatic cancer risk. Findings were consistent within sex, smoking status, and BMI strata or when the case definition was limited to pancreatic adenocarcinoma. Overall, these findings do not support the hypothesis that consumption of dairy foods, calcium, or vitamin D during adulthood is associated with pancreatic cancer risk.

Long-term and baseline recreational physical activity and risk of endometrial cancer: the California Teachers Study.

BACKGROUND: Physical activity may be associated with decreasing endometrial cancer risk; it remains unclear whether the association is modified by body size. METHODS: Among 93 888 eligible California Teachers Study participants, 976 were diagnosed with incident endometrial cancer between 1995-1996 and 2007. Cox proportional hazards regression methods were used to estimate relative risks (RRs) and 95% confidence intervals (CIs) for endometrial cancer associated with long-term (high school through age 54 years) and baseline (3 years prior to joining the cohort) strenuous and moderate recreational physical activity, overall and by body size. RESULTS: Increased baseline strenuous recreational physical activity was associated with decreased endometrial cancer risk (Ptrend=0.006) with approximately 25% lower risk among women exercising >3 h per week per year than among those exercising <1/2 h per week per year (RR, 0.76; 95% CI, 0.63-0.92). This inverse association was observed among overweight/obese women (body mass index ≥25 kg m(-2); Ptrend=0.006), but not among thinner women (Ptrend=0.12). Baseline moderate activity was associated with lower risk among overweight/obese women. CONCLUSION: Increasing physical activity, particularly strenuous activity, may be a lifestyle change that overweight and obese women can implement to reduce their endometrial cancer risk.

The etiology of uterine sarcomas: a pooled analysis of the epidemiology of endometrial cancer consortium.

BACKGROUND: Uterine sarcomas are characterised by early age at diagnosis, poor prognosis, and higher incidence among Black compared with White women, but their aetiology is poorly understood. Therefore, we performed a pooled analysis of data collected in the Epidemiology of Endometrial Cancer Consortium. We also examined risk factor associations for malignant mixed mullerian tumours (MMMTs) and endometrioid endometrial carcinomas (EECs) for comparison purposes. METHODS: We pooled data on 229 uterine sarcomas, 244 MMMTs, 7623 EEC cases, and 28,829 controls. Odds ratios (ORs) and 95% confidence intervals (CIs) for risk factors associated with uterine sarcoma, MMMT, and EEC were estimated with polytomous logistic regression. We also examined associations between epidemiological factors and histological subtypes of uterine sarcoma. RESULTS: Significant risk factors for uterine sarcoma included obesity (body mass index (BMI)≥30 vs BMI<25 kg m(-2) (OR: 1.73, 95% CI: 1.22-2.46), P-trend=0.008) and history of diabetes (OR: 2.33, 95% CI: 1.41-3.83). Older age at menarche was inversely associated with uterine sarcoma risk (≥15 years vs <11 years (OR: 0.70, 95% CI: 0.34-1.44), P-trend: 0.04). BMI was significantly, but less strongly related to uterine sarcomas compared with EECs (OR: 3.03, 95% CI: 2.82-3.26) or MMMTs (OR: 2.25, 95% CI: 1.60-3.15, P-heterogeneity=0.01). CONCLUSION: In the largest aetiological study of uterine sarcomas, associations between menstrual, hormonal, and anthropometric risk factors and uterine sarcoma were similar to those identified for EEC. Further exploration of factors that might explain patterns of age- and race-specific incidence rates for uterine sarcoma are needed.

Obesity, waist size and prevalence of current asthma in the California Teachers Study cohort.

BACKGROUND: Obesity is a risk factor for asthma, particularly in women, but few cohort studies have evaluated abdominal obesity which reflects metabolic differences in visceral fat known to influence systemic inflammation. A study was undertaken to examine the relationship between the prevalence of asthma and measures of abdominal obesity and adult weight gain in addition to body mass index (BMI) in a large cohort of female teachers. METHODS: Prevalence odds ratios (ORs) for current asthma were calculated using multivariable linear modelling, adjusting for age, smoking and race/ethnicity. RESULTS: Of the 88 304 women in the analyses, 13% (n = 11,500) were obese (BMI > or = 30 kg/m(2)) at baseline; 1334 were extremely obese (BMI > or = 40 kg/m(2)). Compared with those of normal weight, the adjusted OR for adult-onset asthma increased from 1.40 (95% confidence interval (CI) 1.31 to 1.49) for overweight women to 3.30 (95% CI 2.85 to 3.82) for extremely obese women. Large waist circumference (>88 cm) was associated with increased asthma prevalence, even among women with a normal BMI (OR 1.37, 95% CI 1.18 to 1.59). Among obese women the OR for asthma was greater in those who were also abdominally obese than in women whose waist was < or = 88 cm (2.36 vs 1.57). Obese and overweight women were at greater risk of severe asthma episodes, measured by urgent medical visits and hospital admissions. CONCLUSIONS: This study confirms the association between excess weight and asthma severity and prevalence, and showed that a large waist was associated with increased asthma prevalence even among women considered to have normal body weight.

Correlates of vitamin supplement use in the United States: data from the California Teachers Study cohort.

OBJECTIVE: To describe factors associated with vitamin supplement use in a large cohort of adult women. METHODS: California teachers and administrators (n = 133,479) completed a questionnaire on lifestyle factors and medical history. Specific supplement users regularly used at least one specific vitamin supplement in the past year; multivitamin users regularly used a multivitamin; and multivitamin and specific supplement users took a multivitamin and one or more specific supplements. Associations between supplement use and other variables were quantified using means, cross-tabulations, and age-adjusted prevalence odds ratios. RESULTS: Multivitamin and specific supplement users tended to be older and Caucasian. Compared to non-users, they were also leaner (odds ratio [OR] for BMI > or = 30 kg/m2 = 0.6 for specific supplement users with or without multivitamins, and OR = 0.7 for multivitamin only users), and were less likely to be current smokers (OR for current smoking = 0.8 for multivitamin plus specific supplement users, OR = 0.9 for specific supplement only users, and OR = 0.7 for multivitamin only users). Specific supplement users (with or without multivitamins) were more likely to use cancer screening tests, eat fruits and vegetables, and exercise than were multivitamin only users or non-users. CONCLUSIONS: A variety of demographic, dietary, and health-related factors were associated with different categories of supplement use.

Phytoestrogen consumption and breast cancer risk in a multiethnic population: the Bay Area Breast Cancer Study.

Research on the relation between phytoestrogens and breast cancer risk has been limited in scope. Most epidemiologic studies have involved Asian women and have examined the effects of traditional soy foods (e.g., tofu), soy protein, or urinary excretion of phytoestrogens. The present study extends this research by examining the effects of a spectrum of phytoestrogenic compounds on breast cancer risk in non-Asian US women. African-American, Latina, and White women aged 35-79 years, who were diagnosed with breast cancer between 1995 and 1998, were compared with women selected from the general population via random digit dialing. Interviews were conducted with 1,326 cases and 1,657 controls. Usual intake of specific phytoestrogenic compounds was assessed via a food frequency questionnaire and a newly developed nutrient database. Phytoestrogen intake was not associated with breast cancer risk (odds ratio = 1.0, 95% confidence interval: 0.80, 1.3 for the highest vs. lowest quartile). Results were similar for pre- and postmenopausal women, for women in each ethnic group, and for all seven phytoestrogenic compounds studied. Phytoestrogens appear to have little effect on breast cancer risk at the levels commonly consumed by non-Asian US women: an average intake equivalent to less than one serving of tofu per week.

Iodine and thyroid cancer risk among women in a multiethnic population: the Bay Area Thyroid Cancer Study.

Research on the relationship between iodine exposure and thyroid cancer risk is limited, and the findings are inconclusive. In most studies, fish/shellfish consumption has been used as a proxy measure of iodine exposure. The present study extends this research by quantifying dietary iodine exposure as well as incorporating a biomarker of long-term (1 year) exposure, i.e., from toenail clippings. This study is conducted in a multiethnic population with a wide variation in thyroid cancer incidence rates and substantial diversity in exposure. Women, ages 20-74, residing in the San Francisco Bay Area and diagnosed with thyroid cancer between 1995 and 1998 (1992-1998 for Asian women) were compared with women selected from the general population via random digit dialing. Interviews were conducted in six languages with 608 cases and 558 controls. The established risk factors for thyroid cancer were found to increase risk in this population: radiation to the head/neck [odds ratio (OR), 2.3; 95% confidence interval (CI), 0.97-5.5]; history of goiter/nodules (OR, 3.7; 95% CI, 2.5-5.6); and a family history of proliferative thyroid disease (OR, 2.5; 95% CI, 1.6-3.8). Contrary to our hypothesis, increased dietary iodine, most likely related to the use of multivitamin pills, was associated with a reduced risk of papillary thyroid cancer. This risk reduction was observed in "low-risk" women (i.e., women without any of the three established risk factors noted above; OR, 0.53; 95% CI, 0.33-0.85) but not in "high-risk" women, among whom a slight elevation in risk was seen (OR, 1.4; 95% CI, 0.56-3.4). However, no association with risk was observed in either group when the biomarker of exposure was evaluated. In addition, no ethnic differences in risk were observed. The authors conclude that iodine exposure appears to have, at most, a weak effect on the risk of papillary thyroid cancer.

Assessing phytoestrogen exposure in epidemiologic studies: development of a database (United States).

BACKGROUND AND OBJECTIVE: Phytoestrogens (weak estrogens found in plants or derived from plant precursors by human metabolism) have been hypothesized to reduce the risk of a number of cancers. However, epidemiologic studies addressing this issue are hampered by the lack of a comprehensive phytoestrogen database for quantifying exposure. The purpose of this research was to develop such a database for use with food-frequency questionnaires in large epidemiologic studies. METHODS: The database is based on consumption patterns derived from semistructured interviews with 118 African-American, Latina, and white women residing in California's San Francisco Bay Area. HPLC-mass spectrometry was used to determine the content of seven specific phytoestrogenic compounds (i.e. the isoflavones: genistein, daidzein, biochanin A, and formononetin; the coumestan: coumestrol; and the plant lignans: matairesinol and secoisolariciresinol) in each of 112 food items/groups. RESULTS: Traditional soy-based foods were found to contain high levels of genistein and daidzein, as expected, as well as substantial amounts of coumestrol. A wide variety of "hidden" sources of soy (that is, soy protein isolate, soy concentrate, or soy flour added to foods) was observed. Several other foods (such as various types of sprouts and dried fruits, garbanzo beans, asparagus, garlic, and licorice) were also found to be substantial contributors of one or more of the phytoestrogens analyzed. CONCLUSIONS: Databases, such as the one described here, are important in assessing the relationship between phytoestrogen exposure and cancer risk in epidemiologic studies. Agencies, such as the United States Department of Agriculture (USDA), that routinely provide data on food composition, on which epidemiologic investigations into dietary health effects are based, should consider instituting programs for the analysis of phytochemicals, including the phytoestrogens.

Sources of phytoestrogen exposure among non-Asian women in California, USA.

OBJECTIVE: We recently described the development of a comprehensive database for assessing phytoestrogen exposure in epidemiologic studies. This paper describes the first application of this database and the primary sources of phytoestrogen consumption in non-Asian women. METHODS: Four hundred and forty-seven randomly selected African-American, Latina, and white women, ages 50-79 years, residing in California's San Francisco Bay Area and participating as controls in an ongoing population-based case-control study of breast cancer, were included in the present analysis. Average daily consumption of each of seven phytoestrogenic compounds was determined for each woman by combining the values from the new database with food consumption reported on a food-frequency questionnaire. RESULTS: Phytoestrogens in the non-Asian Bay Area diet appear to come primarily from: (1) traditional soy-based foods (e.g. tofu and soy milk); (2) "hidden" sources of soy (e.g. foods containing added soy protein isolate, soy concentrate, or soy flour, e.g. many brands of doughnuts and white bread); and (3) a variety of foods which contain only low to moderate amounts of phytoestrogens per 100 grams but which are frequently consumed (e.g. coffee and orange juice). CONCLUSIONS: In the absence of a comprehensive assessment of various phytoestrogens in a wide variety of foods, epidemiologic studies could suffer from the effects of uncontrolled confounding by unmeasured sources of phytoestrogen exposure potentially leading to biased estimates of effect and misinterpretation of findings.

Menstrual and reproductive factors for salivary gland cancer risk in women.

Several observations suggest that salivary gland cancer may be, in part, a hormonally dependent disease. We examined associations between hormonally mediated life events and salivary gland cancer risk in a population-based case-control study. Of 76 women diagnosed between 1989 and 1993, 63 (83%) were interviewed. Of 111 population controls, 83 (75%) were interviewed. Early menarche (OR = 4.1, 95% CI = 1.4-12.1) and nulliparity (OR = 2.6, 95% CI = 1.0-6.7) were associated with increased risk whereas late age at first full-term pregnancy (OR = 0.19, 95% CI = 0.3-1.2) and longer duration of oral contraceptive use (OR = 0.31, 95% CI = 0.10-1.0) were associated with diminished risk. These findings are consistent with a hormonal component in salivary gland cancer risk.

Comparison of methods for classifying Hispanic ethnicity in a population-based cancer registry.

The accuracy of ethnic classification can substantially affect ethnic-specific cancer statistics. In the Greater Bay Area Cancer Registry, which is part of the Surveillance, Epidemiology, and End Results (SEER) Program and of the statewide California Cancer Registry, Hispanic ethnicity is determined by medical record review and by matching to surname lists. This study compared these classification methods with self-report. Ethnic self-identification was obtained by surveying 1,154 area residents aged 20-89 years who were diagnosed with cancer in 1990 and were reported to the registry as being Hispanic or White non-Hispanic. Predictive value positive, sensitivity, and relative bias were used to assess the accuracy of Hispanic classification by medical record and surname. Among those persons classified as Hispanic by either or both of these sources, only two-thirds agreed (predictive value positive = 66%), and many self-identified Hispanics were classified incorrectly (sensitivity = 68%). Classification based on either medical record or surname alone had a lower sensitivity (59% and 61%, respectively) but a higher predictive value positive (77% and 70%, respectively). Ethnic classification by medical record alone resulted in an underestimate of Hispanic cancer cases and incidence rates. Bias was reduced when medical records and surnames were used together to classify cancer cases as Hispanic.

Soy intake and risk of breast cancer in Asians and Asian Americans.

Evidence from case-control studies suggests, although not entirely consistently, that soy intake may protect against breast cancer. The designs and findings of studies conducted in Asian women living in Japan, Singapore, China, and the United States are reviewed. Because of the considerably higher intake of soy by native Asians than by Asian Americans living in California and Hawaii, these studies investigated different segments of the dose-response relation between soy intake and breast cancer risk. Data are not sufficient to determine the amount or frequency of soy intake effective in protecting against breast cancer. Of concern is that soy intake may be homogeneously high in Asia, making it difficult to identify differences in breast cancer risk between high and moderate daily consumers. In studies conducted in Asian Americans, it is difficult to be certain that soy intake is not a marker of other factors related to Western lifestyle that are causally associated with risk of breast cancer. Additional studies assessing the role of soy and breast cancer are needed. These studies should assess intake of all food sources of soy, considering portion size as well as other dietary and nondietary factors that may confound the soy-breast cancer association. A better understanding of the mechanisms whereby soy intake may influence the risk of breast cancer is also needed. Dietary intervention studies with soy will provide information on the acute effects of soy on endogenous hormone concentrations. Cross-sectional and longitudinal studies are necessary to investigate the longer-term relations between hormone concentrations and soy intake in women.

Adjustment of cancer incidence rates for ethnic misclassification.

Although ethnic population counts measured by the United States Census are based on self-identification, the same is not necessarily true of cases reported to cancer registries. The use of different ethnic classification methods for numerators and denominators may therefore lead to biased estimates of cancer incidence rates. The extent of such misclassification may be assessed by conducting an ethnicity survey of cancer patients and estimating the proportion misclassified using double sampling models that account for sample stratification. For two ethnic categories, logistic regression may be used to model self-identified ethnicity as a function of demographic variables and the fallible classification method. Incidence rates then may be adjusted for misclassification using regression results to estimate the number of cancer cases of a given age, sex, and site in each self-identified ethnic group. An example is given using this method to estimate ethnic misclassification of San Francisco Bay area Hispanic cancer patients diagnosed in 1990. Results suggest that the number of cancer cases reported as Hispanic is an underestimate of the number of cases self-identified as Hispanic, resulting in an underestimate of Hispanic cancer rates.

Absence of Epstein-Barr virus EBER-1 transcripts in an epidemiologically diverse group of breast cancers.

Epstein-Barr virus (EBV), a ubiquitous herpesvirus associated with certain lymphomas and carcinomas, has been identified within the malignant cells of a small proportion of breast tumors. As breast cancer is a very common malignancy in women, a pathogenetic role of EBV for even a subgroup of patients could have important implications for etiology and prevention. Therefore, we attempted to confirm the EBV-breast cancer association by exploring it in a representative case series stratified by characteristics that modify breast cancer risk. We studied a sample of 97 female and 28 male patients identified from a US population-based cancer registry. Patients were selected randomly within age, sex, ethnicity and tumor estrogen-receptor status groups. With their archived tumor tissues, we examined EBV presence using in situ hybridization for the EBER-1 transcript. In the 107 technically adequate specimens, we did not detect this viral transcript in any tumors, including one from a woman who also had an EBER-positive nasopharyngeal carcinoma. Our uniformly negative findings are extremely unlikely to have occurred by chance and cannot be attributed to selective sampling, as our study group included persons at diverse risk for breast cancer. We conclude that the EBV EBER-1 transcript is not commonly expressed in breast cancer, based on a broadly representative case series, though we cannot exclude an association of EBV within a particular population subgroup.

Environmental factors and the risk of salivary gland cancer.

Cancer of the major salivary glands is rare, and little is known about its etiology. We conducted a population-based case-control study to elucidate the risk factors for these tumors. Of 199 cases diagnosed with salivary gland tumors between 1989 and 1993, 150 (75%) were interviewed. We subsequently excluded nine cases based on review of pathology specimens. We identified 271 controls through random-digit dialing and the Health Care Finance Administration files; 191 (70%) were interviewed. Therapeutic medical radiation treatment to the head or neck [odds ratio (OR) = 2.6; 95% confidence interval (CI) = 0.84-8.1], full mouth dental x-rays (OR = 1.6; 95% CI = 1.0-2.7), and ultraviolet light treatment to the head or neck (OR = 1.9; 95% CI = 0.89-4.3) were associated with increased risk. These elevations in risk were largely limited to those exposed before 1955, when the exposure dose was substantially higher. Occupational exposure to radiation/radioactive materials (OR = 2.4; 95% CI = 1.0-5.4) and nickel compounds/alloys (OR = 6.0; 95% CI = 1.6-22.0), as well as employment in the rubber industry (OR = 7.0; 95% CI = 0.80-60.3), increased risk. In men, current smoking (OR = 2.1; 95% CI = 0.98-4.7) and heavy alcohol consumption (OR = 2.5; 95% CI = 1.1-5.7) were associated with risk, but these factors were not strongly related to salivary gland cancer in women.

Diet and the risk of salivary gland cancer.

Cancer of the major salivary glands is relatively rare, and little is known about its etiology. The only established risk factors are radiation exposure and a prior cancer. The role of diet in the development of salivary gland tumors has not been addressed previously. The results from a population-based case-control study conducted in the greater San Francisco-Monterey Bay area examining the association between dietary intake and salivary gland cancer risk are presented. Of 199 cases diagnosed with salivary gland tumors between 1989 and 1993, 150 (75%) were interviewed. Nine cases were subsequently excluded based on review of pathology specimens. Of 271 controls identified through random-digit dialing and the Health Care Finance Administration files, 191 (70%) were interviewed. Eight cases and seven controls who over- or underreported dietary intake were excluded from analysis. Vitamin C intake of > 200 mg/day compared with < or = 100 mg/day was associated with a 60% decrease in salivary gland cancer risk (odds ratio (OR) = 0.40, 95% confidence interval (CI) 0.22-0.70). Inverse associations observed for carotene, vitamin E, and fiber from fruits and vegetables were diminished when adjusted for vitamin C intake. Fiber from been sources was associated with a 51% decrease in risk after adjusting for vitamin C intake (OR = 0.49, 95% CI 0.26-0.92 for > 1.4 g/day compared with < or = 0.4 g/day). Cholesterol intake was associated with elevated risk (OR = 1.67, 95% CI 1.2-2.4 for a 10% increase in calories from cholesterol). These findings suggest that preventive strategies developed for common chronic diseases, such as increased consumption of fruits and vegetables and limiting foods high in cholesterol, also may be effective in preventing these rare tumors.

Urinary phytoestrogen levels in young women from a multiethnic population.

Phytoestrogens include several classes of chemical compounds (i.e., isoflavones, coumestans, and lignans) which are structurally similar to endogenous estrogens. In biological systems, they have both estrogenic and antiestrogenic effects and may reduce the risk of developing certain types of hormonally related diseases. However, little information is available on population differences in exposure to phytoestrogens. To examine racial/ethnic differences in urinary phytoestrogen levels, 50 young women (ages 20-40 years) were randomly selected from participants in a previous epidemiological study in which 24-h urine specimens and a dietary assessment were obtained. Subjects were members of the Kaiser Permanente Medical Care Program of northern California. Selection was stratified on race/ethnicity. Urinary levels of seven phytoestrogens were measured using high-performance liquid chromatography-mass spectrometry. Substantial variation in phytoestrogen levels was observed and racial/ethnic differences are described. The highest levels of coumestrol and the lignans were observed in white women and the lowest levels in Latina and African American women. Genistein levels, however, were highest in Latina women; other isoflavone levels did not differ significantly by race/ethnicity.

Predictors of misclassification of Hispanic ethnicity in a population-based cancer registry.

PURPOSE: Hispanic ethnicity is often used as a category for calculating population-based rates or assessing risk of epidemiologic studies. However, ethnic misclassification can lead to false conclusions unless the extent of misclassification and the characteristics of those misclassified are understood. METHODS: This study explored determinants of ethnic misclassification in a sample of 1154 cancer cases in the San Francisco-Oakland cancer registry, where ethnic classification is based on surname or medical record report. We compared the following: correctly classified Hispanics, persons classified as Hispanic who self-identified as non-Hispanic, and persons classified as non-Hispanic who self-identified as Hispanic. RESULTS: Among men classified as Hispanic, those most likely to self-identify as non-Hispanic did not speak Spanish, had non-Spanish surnames, and were recent immigrants. Women misclassified as Hispanic did not speak Spanish or have Spanish maiden names, nor did they have mothers with Spanish maiden names. Persons who called themselves Hispanic, but were misclassified by the registry, were likely to be non-Spanish speaking college-education males. CONCLUSIONS: Researchers using ethnicity should be aware of how ethnicity was determined and how this classification may bias or confound their results.

Tofu and risk of breast cancer in Asian-Americans.

Breast cancer rates among Asian-Americans are lower than those of US whites but considerably higher than rates prevailing in Asia. It is suspected that migration to the US brings about a change in endocrine function among Asian women, although reasons for this change remain obscure. The high intake of soy in Asia and its reduced intake among Asian-Americans has been suggested to partly explain the increase of breast cancer rates in Asian-Americans. We conducted a population-based case-control study of breast cancer among Chinese-, Japanese-, and Filipino-American women in Los Angeles County MSA, San Francisco Oakland MSA, and Oahu, Hawaii. Using a common questionnaire which assessed frequency of intake of some 90 food items, 597 Asian-American women (70% of those eligible) diagnosed with incident, primary breast cancer during 1983-1987 and 966 population-based controls (75% of those eligible) were interviewed. Controls were matched to cases on age, ethnicity, and area of residence. This analysis compares usual adult intake of soy (estimated primarily from tofu intake) among breast cancer cases and control women. After adjustment for age, ethnicity and study area, intake of tofu was more than twice as high among Asian-American women born in Asia (62 times per year) compared to those born in the US (30 times per year). Among migrants, intake of tofu decreased with years of residence in the US. Risk of breast cancer decreased with increasing frequency of intake of tofu after adjustment for age, study area, ethnicity, and migration history; the adjusted OR associated with each additional serving per week was 0.85 (95% CI = 0.74-0.99). The protective effect of high tofu intake was observed in pre- and postmenopausal women. This association remained after adjustment for selected dietary factors and menstrual and reproductive factors. However, this study was not designed specifically to investigate the role of soy intake and our assessment of soy intake may be incomplete. We cannot discount the possibility that soy intake is a marker of other protective aspects of Asian diet and/or Asian lifestyle.