Norman F. Boyd

Fish consumption and breast cancer risk: an ecological study

There is experimental evidence that fish oils protect against mammary carcinogens in animals. However, there has been little investigation of the possible relevance of this finding to breast cancer in humans. We compared breast cancer incidence and mortality rates with estimates of the consumption of fish and other foods and nutrients in the countries for which reliable data are available. The results showed an inverse association between percent calories from fish and breast cancer rates that was consistent with a protective effect. This analysis confirmed the finding of others that dietary fat is strongly associated with international variation in breast cancer rates. It also showed that of the dietary components considered, percent calories from fish was the factor most strongly correlated with breast cancer rates after statistical adjustment for dietary fat intake. This result is therefore in accord with animal experimental data and suggests that the omega-3 fatty acids contained in certain fish may protect against breast cancer.

Plasma lipids in premenopausal women with mammographic dysplasia.

Epidemiological evidence indicates that mammographic dysplasia is associated with an increased risk of breast cancer, particularly in premenopausal women. To examine biochemical associations with mammographic dysplasia we have compared premenopausal women with different patterns of the breast parenchyma on mammography. One group had extensive radiological dysplasia (n = 30) and the other no dysplasia (n = 16). Both groups were recruited from mammographic units in the same way and then compared according to epidemiological risk factors, anthropometric measures, nutrient intake and plasma levels of oestradiol, progesterone and prolactin obtained in both follicular and luteal phases of the menstrual cycle as well as total plasma cholesterol and lipid fractions. Women with mammographic dysplasia were found to be leaner, more often nulliparous and to consume more alcohol than women without these radiological changes. Mammographic dysplasia and a family history of breast cancer were found to be independently associated with significantly higher levels of high density lipoprotein cholesterol (HDL-C) after taking into account the possible confounding effects of percentage body fat, parity and consumption of alcohol and dietary fat. Triglyceride levels were also independently associated with a family history of breast cancer. We conclude that further investigation is warranted of the role of plasma lipids in relation to breast cancer risk.

A review of the methods used by studies of dietary measurement.

Studying the association between diet and disease requires reliable and valid methods for the assessment of diet. The authors reviewed the literature concerned with the assessment of these aspects of the measurement of dietary intake. Studies were examined for the stated purpose and scope of the dietary instrument, for a description of the instrument itself, for any methods employed to train individuals in its use and for the methods used to assess its reliability and validity. Of the 59 studies reviewed, 54% described fully the dietary method used. Of the 39 studies that described the results using questionnaires, 51% gave specific information on questions asked and only 18% included the questionnaire itself. Reliability was assessed in 26 studies and 74% (19) used the test-retest reliability and 22% (6) used proxies to assess reliability. Validity was assessed in 46 studies and 83% (38) used indirect methods that compared the results of one dietary method (e.g. 24 hr recall) with another more extensive one (e.g. diet history). Thirty five percent (16) used biochemical and 15% (7) used other methods. This review suggests several directions that might be usefully followed in conducting and reporting further research in the development of methods to assess diet.

THE FEASIBILITY OF TESTING EXPERIMENTALLY THE DIETARY FAT-BREAST CANCER HYPOTHESIS

Experimental evidence, derived from controlled clinical trials in which the range of fat intake is increased beyond that seen in most Western populations, is capable of overcoming this limitation of observational epidemiology, and would provide the strongest evidence available for the relationship of dietary fat intake to breast cancer risk. Furthermore, such trials are the only means likely to answer the question of whether breast cancer risk in high risk subjects can be modified by changing dietary fat intake

Bias and the association of mammographic parenchymal patterns with breast cancer.

We have carried out a case-control study to evaluate the association between Wolfes mammographic patterns and the risk of breast cancer, and to examine the influence of control selection and the radiologist who read the films upon the results obtained. Mammograms of the non-cancerous breast of 183 women with unilateral breast cancer were compared with mammograms from two age-matched control groups: a group of asymptomatic women attending a screening centre, and a group of symptomatic women referred for the diagnostic evaluation of suspected breast disease. Films were arranged in random sequence and independently classified by 3 radiologists. A strong and statistically significant association was found between mammographic dysplasia and breast cancer when controls from the screening centre were compared to cases, but not when cases were compared to women referred for the diagnostic evaluation of breast disease. This result appears to arise in part because of an association between symptoms of benign breast disease and mammographic dysplasia, and suggests that some previous negative studies of the association of mammographic patterns with breast cancer may have arisen from the inclusion of symptomatic subjects as controls.

Cyclical mastopathy: An evaluation of methods of assessment

We have evaluated three methods of assessing patients with cyclical breast symptoms (cyclical mastopathy--CM). One method, a screening questionnaire, was used to identify women with CM, and two others, a symptom severity questionnaire and a daily diary, were used prospectively to record the severity of symptoms in relation to the menstrual cycle. The screening questionnaire was assessed for test-retest reliability and for agreement between the recalled severity of symptoms and those recorded during prospective measurement. The symptom severity questionnaire and diary were assessed by examining their ability to discriminate between pre- and postmenstrual phases of the menstrual cycle, differences in symptom severity at these times being the cardinal feature of CM. Test-retest reliability of premenstrual symptoms by the screening questionnaire gave correlation coefficients over 0.70 for 9 of the 11 items assessed. The symptom severity questionnaire showed significant differences between pre- and post-menstrual scores for 8 of the 11 items assessed and the diary for each of the 2 items assessed. Comparison of symptom severity as recalled and as prospectively recorded showed only modest agreement. These results show that the instruments used to assess symptom severity performed satisfactorily but that the screening questionnaire used to identify women with CM, although reliable, correlated only moderately well with prospective measurement.