Science Editor

Editor's note: Science Scan is a roundup of recently published biotechnology-relevant research.

Measurement error of diet is a major problem when examining associations between diet and disease endpoints such as cancer. A report in The Lancet dated July 19, 2003, is titled "Are imprecise methods obscuring a relation between fat and breast cancer?" Its authors are nutritionists at the University of Cambridge (UK) School of Clinical Medicine.

It makes the point that results of studies in which biological markers have been used as the reference method for assessment of dietary intake for selected nutrients suggest that the degree of error associated with food-frequency questionnaires (FFQs) is considerably larger than previously estimated. This could explain the lack of an association in population studies between increased fat intake and breast cancer.

The authors assessed that relation with an FFQ, similar to those used in population cohort studies, together with a seven-day food diary completed by women in a large-scale European survey. Some 13,000 participants were studied using those two questionnaires between 1993 and 1997. Of them, 168 women developed breast cancer by the year 2000. At that time, analysis of fat intake was assessed for each of the patients compared with four healthy controls matched for age and other factors to take account of possible bias.

Women in the upper 20 percent for saturated-fat consumption were at twice the risk of breast cancer over those in the lower percentile when fat intake was assessed by the seven-day food diary. However, no association was evident with use of the FFQ.

The lead author commented: "Inconsistency between experimental and epidemiological data on fat and breast-cancer risk could thus be accounted for by problems with methods used in cohort studies to measure diet. The food diary is more expensive to code for conversion into nutrients than the FFQ, but we have shown that its use is acceptable and feasible in large cohort studies.

"No biomarkers exist for fat intake," she concluded, "so none of the associations shown can be said to be free of measurement-error effects. However, our preliminary findings suggest that use of the food diary can detect relations between diet and cancer risk within a relatively homogeneous population."

An accompanying editorial from the Fred Hutchinson Cancer Research Center in Seattle observed, "The Lancet article highlights the importance of the methodological issues in nutrition and chronic disease research by providing an example in which two valuable dietary self-reported instruments give qualitatively different results.

"Their report," it added, "will help to move the debate about measurement error in dietary assessment, which has been ongoing to several years, into a more practical arena. However, it will be useful to compare disease-risk associations with food-diary and food-frequency assessments of fat intake in additional cohort studies. More generally, the reliability and interpretation of cohort study data on the controversial topic of an association between dietary fat and breast cancer will unfortunately remain unclear until further objective information becomes available."

Results From Clinical Trials Of Iressa EGFR Compound Reported In Journal Oncologist

The Oncologist is a bimonthly international peer-reviewed journal for physicians devoted to cancer patient care. Its latest issue, for August 2003, caries an article written by the U.S. Food and Drug Administration titled "FDA drug approval summary: Gefitinib (ZD1839) (Iressa) tablets." Iressa is trademarked by AstraZeneca plc in London.

Iressa received accelerated approval from the FDA as a monotherapy treatment for patients with locally advanced or metastasic non-small-cell lung cancer. This article highlights the results of clinical trials that demonstrate the effectiveness and safety of gefitinib. The trials included males and females, smokers and nonsmokers. The authors offer detailed results of these trials, recommended dosage and possible side effects of the drugs.

"Iressa is a member of a new class of molecularly targeted cancer drugs," the article's lead author explained. It was developed to block growth stimulatory signals mediated by cellular tyrosine kinases, including epidermal growth factor receptor (EGFR). Disruption of these signals interferes with cancer cell proliferation.

Bacteria's Formidable Sexual Promiscuity Confers Genomic Advantages Over Other Living Species

The concept of chromosomes with a ring structure was born during the early studies of bacterial sexuality, along with the discovery of fertility factors, later provided the key tools for gene cloning and biotechnology. But the plasmid-mediated transfer of antibiotic and other resistances, as well as pathogenicity, has served bacteria well in their own adaptive resolution.

Science, dated Aug. 8, 2003, carries a brief review of the subject titled "Bacterial sex: Playing voyeurs 50 years later." Its French authors are geneticists at the University of Paris.

"Although in the shadow cast by the 50th anniversary of DNA structure," their paper observed, "the half-century anniversary of the discovery of bacterial sexuality must not pass unnoticed." It continued, "Bacterial sex is extremely important to bacteria themselves. In the evolutionary past, horizontal gene transfer and recombination have shaped bacterial genomes, which appear as complex mosaics composed of genes from different lineages, species and genera.

"Formidable promiscuity," the paper concludes, "has given bacteria a unique advantage over other creatures because it provides an awesome mechanism for ongoing adaptive evolution - a sort of permanently and rapidly evolving communal genome.

"More generally," the report concluded, "the reliability and interpretation of cohort study data on the controversial topic of an association between dietary fat and breast cancer will unfortunately remain unclear until further objective information becomes available about the measurement properties of the dietary assessment methods used."