Coffee drinking: the rationale for treating it as a potential effect modifier of carcinogenic exposures

Clinical and epidemiological studies on cancer etiology seldom treat coffee drinking as a potential effect modifier. Yet caffeine exerts significant effects upon a large variety of physiologic, cellular and molecular systems. Caffeine, 'the world's most popular drug', is also a fundamental research tool, widely used in clinical studies on drug metabolism, and in experimental studies on cell cycle checkpoints, DNA repair, and apoptosis, among many other. Caffeine can profoundly alter cell cycle checkpoint function and several mechanisms of DNA repair, as well as carcinogen metabolism. The impact of caffeine on cell cycle checkpoint function occurs in spite of it being nonmutagenic in traditional mutagenesis assays. A complex body of biologic evidence suggests that caffeine-containing beverages can both enhance and antagonise potentially carcinogenic exposures. However, most pathways leading to the ultimate effects in human beings remain unknown. It is unclear whether any of the hundreds of compounds contained in coffee and tea exert a direct and significant carcinogenic effect per se in any human tissue at usual conditions of use. Reasons exist to consider that coffee may sometimes be an indirect, positive confounder. The study of interactions between caffeine-containing beverages and environmental agents in well defined groups of healthy and diseased people could yield new insights into checkpoint signal transduction and other mechanisms of carcinogenesis. Information on the use of caffeine-containing beverages should more often be integrated in studies on the role of gene-environment interactions in the pathogenesis of cancer.

Worsening of hypertension in a pregnant woman with renal arteriovenous malformation: a successful superselective embolization after delivery

A 30-year-old female presented with uncontrolled hypertension due to arteriovenous malformation in the upper third of the right kidney, which worsened during pregnancy. The arteriovenous malformation was detected by color-coded Doppler sonography, confirmed by angiography, and the fistula was sealed by superselective arterial embolization with metallic coils. Superselective embolization is the most effective and safe treatment for this rare and complex pathology.

Effects of protein kinase C inhibition and activation on proliferation and apoptosis of bovine retinal pericytes

AIMS/HYPOTHESIS

Drop-out of capillary pericytes occurs early and selectively in diabetic retinopathy. High glucose concentrations decrease replication and increase apoptosis of cultured pericytes. Since glucose activates protein kinase C, we investigated the effects of modulating this intracellular mediator on replication, cell cycle and apoptosis of cultured bovine retinal pericytes.

METHODS

Pericytes cultured in 5.6 or 28 mmol/l glucose were exposed to a protein kinase C activator (phorbol 12-myristate 13-acetate) and/or a selective inhibitor of its beta2 isoform (LY379196). Cells were counted after 7 days. Proliferation by the tetrazolium to formazan assay and DNA synthesis by 5-bromo-2'-deoxyuridine incorporation were measured at day 4. Cell cycle by flow cytometry and apoptosis by ELISA were assessed at day 2.

RESULTS

High glucose reduced pericyte replication and increased apoptosis. Protein kinase C activation increased proliferation, while inhibition of its beta2 isoform decreased it. Cell cycle was accelerated by protein kinase C activation and delayed by inhibition. Apoptosis was enhanced by protein kinase C inhibition and reduced by activation.

CONCLUSIONS/INTERPRETATION

Protein kinase C inhibition amplifies the anti-proliferative and pro-apoptotic effects of high glucose on cultured pericytes, whereas stimulation reduces apoptosis and promotes proliferation both in physiological glucose and high glucose. Protein kinase C inhibition, proposed for the treatment of diabetic macular edema and proliferative retinopathy, might accelerate pericyte dropout in earlier stages when these cells are still present in retinal capillaries.

A study of capillary pericyte viability on extracellular matrix produced by endothelial cells in high glucose

AIMS/HYPOTHESIS

Thickening of the basement membrane and selective loss of pericytes occur early in diabetic retinopathy. As we showed previously that pericyte adhesion is impaired on extracellular matrix produced by endothelial cells in high hexose concentrations, we aimed to verify if altered adhesion could influence pericyte viability and replication.

METHODS

Conditioned extracellular matrices were obtained by growing human umbilical vein endothelial cells in media containing 28 mmol/l D-glucose, with or without the inhibitors of protein glycation thiamine or aminoguanidine, and D-galactose or L-glucose up to 28 mmol/l. Having removed the endothelium, bovine retinal pericytes were grown on these matrices and, in separate experiments, on laminin, fibronectin or type IV collagen. Pericyte viability and replication were measured by cell counts and DNA synthesis after 7 days, cell cycle traversal after 2 days and apoptosis after 18 h, 2 days and 7 days.

RESULTS

Pericyte counts and DNA synthesis were reduced on matrices produced in high D-glucose and D-galactose, whilst matrix obtained in L-glucose reduced DNA synthesis but not counts. Both thiamine and aminoguanidine corrected reduced pericyte viability when added to high D-glucose. Cell cycle and apoptosis were not affected by growing pericytes on different conditioned matrices. Laminin, fibronectin and type IV collagen did not modify pericyte replication.

CONCLUSIONS/INTERPRETATIONS

Reduced pericyte counts could depend on impaired initial adhesion to the extracellular matrix produced by endothelium in high hexose concentrations, rather than impaired replication or viability. Altered cell-matrix interactions might facilitate pericyte dropout in diabetic retinopathy, independently of the effects of high glucose on pericyte replication.

Diabetic retinopathyA clinical update

Easy observation of the fundus oculi makes retinopathy the most frequently reported chronic complication of diabetes and, consequently, the one we know best in terms of epidemiology and natural history. Achieving near-normal levels of blood glucose and blood pressure provides empirical though powerful tools for clinicians to delay the onset and progression of diabetic retinopathy. Even when these measures have failed and retinopathy becomes sight-threatening, laser photocoagulation has proven remarkably effective. Nonetheless, retinopathy remains a leading cause of blindness and there is little evidence that diabetes-related visual loss is decreasing in industrialized countries. This may result from the mixed blessing of prolonged survival of patients who had become diabetic when metabolic control was pursued less fastidiously than today. Screening for sight-threatening retinopathy is the most cost-effective medical procedure known and should help optimise the use of diagnostic and therapeutic resources, but its widest deployment still meets with inertia and lack of interest within most health care systems. Improving clinical skills and technology, however, allow us to take a more optimistic look at the future, as pathogenesis-targeted forms of treatment are being developed and tested through appropriately powered clinical trials.

Failure of angiotensin II and insulin to stimulate transforming growth factor-beta1. Release from cultured bovine retinal pericytes

BACKGROUND

Activation of the renin-angiotensin system (RAS) may induce cardiovascular and renal fibrosis in hypertension and diabetes. This fibrogenic effect is mainly mediated by Transforming Growth Factor-B1 (TGF-B1), a multifunctional citokyne released by endothelial, vascular smooth muscle and renal mesangial cells, that is able to increase extracellular matrix deposition. Retinal capillary pericytes have functions similar to those of mesangial cells, including ability to synthesize and release TGF-B1 and produce extracellular matrix. An intraocular RAS was described in the human eye and may produce effects similar to those observed in the heart and kidney, which could be mediated by TGF-B1. In particular, TGF-B1 might be involved in thickening of the capillary basement membrane in diabetic microangiopathy. We therefore aimed at evaluating the possible effects of Angiotensin-II on TGF-B1 secretion by cultured retinal pericytes (BRP).

METHODS

BRP cultures were incubated with Angiotensin-II or insulin (known to play a permissive effect on TGF-B1 release from mesangial cells) or Angiotensin-II + insulin at final concentrations of 10-10, 10-8, 10-6, 10-4 mol/L.

RESULTS

Baseline TGF-B1 concentrations in the supernatants of pericyte cultures were 6 139 +/- 1 919 pg/mL/106 cells; no changes of TGF-B1 concentrations resulted from adding increasing amounts of Ang II, insulin or both.

CONCLUSIONS

Though confirming that cultured bovine retinal pericytes spontaneously release TGF-B1, Angiotensin-II did not produce any stimulatory effects of in our experimental system

Perceptions of diabetic retinopathy and screening procedures among diabetic people

AIMS

To assess how diabetic patients perceive retinopathy, screening for sight-threatening lesions and their own role in preventing blindness.

METHODS

A questionnaire was administered to 258 consecutive patients after screening for retinopathy, according to the European Field Guide-Book procedure, in Turin (n = 130) and Wales (n = 128, W). All Welsh patients and 70 in Turin (T1) were on standard diabetes care at their clinic or general practitioner, whereas 60 in Turin (T2) were on permanent group education.

RESULTS

According to 65%, 84% and 100% of patients in W, T1 and T2, respectively, diabetes may damage the eyes. Retinopathy had been heard of by 48% (W), 67% (T1) and 100% (T2). In T2, 82% of patients could give a meaningful description of retinopathy but only 17% could use correctly the word 'retina'. In W and T1, 16% and 19% could describe retinopathy but none could describe the retina. In W and T1, 47% and 57% believed they could not help with eye care, whereas 78% in T2 replied that they should control diabetes and 20% that eyes should be checked regularly. Regarding reasons for screening, 100% of patients in T2 answered 'prevention and checks', against 61% in T1 and only 9% in W. In T1 and W, 33% and 37% did not know why they were being screened.

CONCLUSIONS

Patients' health perceptions and internal control mechanisms may be insufficiently developed for optimal participation in retinopathy screening. Diabetes care by long-term group education may address this problem.

Clinical assessment of dysphagia in early phases of Parkinson's disease

Dysphagia is a frequent symptom in parkinsonism, but it is less commonly reported by patients with idiopathic Parkinson's disease (IPD), especially in the early phases. Sixty-five patients with IPD were questioned about symptoms of dysphagia and an objective swallowing test was administered. Reduced swallowing speed for food and complaints of food sticking in the throat, wet voice and cough after liquid intake and nocturnal sialorrhea were reported, respectively, by 35%, 20% and 15% of patients. On objective examination, oral-phase (facial, tongue and palatal musculature) abnormalities were found in 70% of patients. Lingual transfer movements, mainly propulsion, and palatal elevation were severely hypokinetic. Wet voice after liquid intake and cough reflex after solid/liquid intake were detected in 40% of patients. On the other hand, severe dysphagia with frequent food aspiration and chest infections requiring antibiotics in the last 12 months was not found; cough reflex was retained in all patients. On the basis of these results, a regular assessment on swallowing abilities in patients with IPD is warranted in the clinical setting because with simple dietary advice and a short rehabilitative training, the quality of life in these patients can be improved.

Lifestyle intervention by group care prevents deterioration of Type II diabetes: a 4-year randomized controlled clinical trial

AIMS/HYPOTHESIS

Metabolic control worsens progressively in Type II (non-insulin-dependent) diabetes mellitus despite intensified pharmacological treatment and lifestyle intervention, when these are implemented on a one-to-one basis. We compared traditional individual diabetes care with a model in which routine follow-up is managed by interactive group visits while individual consultations are reserved for emerging medical problems and yearly checks for complications.

METHODS

A randomized controlled clinical trial of 56 patients with non-insulin-treated Type II diabetes managed by systemic group education and 56 control patients managed by individual consultations and education.

RESULTS

Observation times were 51.2+/-2.1 months for group care and 51.2+/-1.8 for control subjects. Glycated haemoglobin increased in the control group but not in the group of patients ( p<0.001), in whom BMI decreased ( p<0.001) and HDL-cholesterol increased ( p<0.001). Quality of life, knowledge of diabetes and health behaviours improved with group care ( p<0.001, all) and worsened among the control patients ( p=0.004 to p<0.001). Dosage of hypoglycaemic agents decreased ( p<0.001) and retinopathy progressed less ( p<0.009) among the group care patients than the control subjects. Diastolic blood pressure ( p<0.001) and relative cardiovascular risk ( p<0.05) decreased from baseline in group patients and control patients alike. Over the study period, group care required 196 min and 756.54 US dollars per patient, compared with 150 min and 665.77 US dollars for the control patients, resulting in an additional 2.12 US dollars spent per point gained in the quality of life score.

CONCLUSION/INTERPRETATION

Group care by systemic education is feasible in an ordinary diabetes clinic and cost-effective in preventing the deterioration of metabolic control and quality of life in Type II diabetes without increasing pharmacological treatment.

Family history of cancer and germline BRCA2 mutations in sporadic exocrine pancreatic cancer

BACKGROUND

Hereditary factors have been reported in 5-10% of cases with exocrine pancreatic cancer and recent data support a role for BRCA2.

AIMS

We have studied the prevalence of germline BRCA2 mutations in two groups of patients with exocrine pancreatic cancer from an unselected series in Spain: group A included 24 cases showing familial aggregation of cancer and group B included 54 age, sex, and hospital matched cases without such evidence.

METHODS

Information was obtained by interview of patients and was validated by a telephone interview with a structured questionnaire. In patients from group A, >80% of the coding sequence of BRCA2 was analysed; in patients from group B, the regions in which germline BRCA2 mutations have been described to be associated with pancreatic cancer were screened.

RESULTS

Telephone interviews led to reclassification of 7/54 cases (13%). Familial aggregation of cancer was found in 24/165 cases (14.5%); six patients had a first degree relative with pancreatic cancer (3.6%) and nine patients had relatives with breast cancer. Germline BRCA2 mutations were not identified in any patient from group A (0/23). Among group B cases, one germline variant (T5868G>Asn1880Lys) was found in a 59 year old male without a family history of cancer. The 6174delT mutation was not found in any of the 71 cases analysed.

CONCLUSIONS

The overall prevalence of BRCA2 mutations among patients with pancreatic cancer in Spain is low and the 6174delT mutation appears to be very infrequent. Our data do not support screening patients with cancer of the pancreas for germline BRCA2 mutations to identify relatives at high risk of developing this tumour.

Differential activation by Ca2+, ATP and caffeine of cardiac and skeletal muscle ryanodine receptors after block by Mg2+

The block of rabbit skeletal ryanodine receptors (RyR1) and dog heart RyR2 by cytosolic [Mg2+], and its reversal by agonists Ca2+, ATP and caffeine was studied in planar bilayers. Mg2+ effects were tested at submaximal activating [Ca2+] (5 microM). Approximately one third of the RyR1s had low open probability ("LA channels") in the absence of Mg2+. All other RyR1s displayed higher activity ("HA channels"). Cytosolic Mg2+ (1 mM) blocked individual RyR1 channels to varying degrees (32 to 100%). LA channels had residual P(o) <0.005 in 1 mM Mg2+ and reactivated poorly with [Ca2+] (100 microM), caffeine (5 mM), or ATP (4 mM; all at constant 1 mM Mg2+). HA channels had variable activity in Mg2+ and variable degree of recovery from Mg2+ block with Ca2+, caffeine or ATP application. Nearly all cardiac RyR2s displayed high activity in 5 microM [Ca2+]. They also had variable sensitivity to Mg2+. However, the RyR2s consistently recovered from Mg2+ block with 100 microM [Ca2+] or caffeine application, but not when ATP was added. Thus, at physiological [Mg2+], RyR2s behaved as relatively homogeneous Ca2+/caffeine-gated HA channels. In contrast, RyR1s displayed functional heterogeneity that arises from differential modulatory actions of Ca2+ and ATP. These differences between RyR1 and RyR2 function may reflect their respective roles in muscle physiology and excitation-contraction coupling.

[Concentrations of persistent toxic compounds in the Spanish population: a puzzle without pieces and the protection of public health]

The contamination by persistent toxic compounds (PTCs) of the general population is a fact of relevance from a public health perspective. It is also relevant to health care professionals, as well as for environmental, food, industrial and economic policies. Though in Spain information on food contamination by PTCs shows large time and geographic gaps, the scarcity of data is even more severe on the concentrations that PTCs have in people: a representative study of a general healthy population living in a wide geographic area has never been conducted in the country. However, the available studies indicate that around 80-100% of the population has detectable concentrations of DDE, PCBs, hexachlorbenzene or lindane. Studies on the effects that PTCs have upon humans are extremely infrequent in Spain. Yet, the international literature suggests that some PTCs may induce significant biological and clinical effects at doses below those traditionally deemed "safe". The mechanism of action of PTCs are not restricted to endocrine disruption. Assessing the clinical and social relevance of the more subtle and long-term effects of PTCs presents interesting challenges and opportunities. Spain and other European countries lack population indicators on the impact that environmental processes have on human health. Several government levels have a role to fulfill in the monitoring of biological levels of PTCs among persons in order to assess the risks of adverse health effects. Along with over a hundred other countries. Spain will soon try to implement the Stockholm treaty on persistent organic pollutants (POPs). This constitutes a new opportunity to develop more efficient policies to control PTC residues in food, humans and the environment. As part of the treaty implementation it is necessary to launch a Report on factors that influence body concentrations of PTCs in the Spain general population.

Pericyte adhesion is impaired on extracellular matrix produced by endothelial cells in high hexose concentrations

AIMS/HYPOTHESIS

Thickening of the basement membrane and selective loss of pericytes are early events in diabetic retinopathy. We aimed at checking whether pericyte interaction with extracellular matrix produced by endothelial cells is influenced by the hexose concentrations in which endothelial cells are cultured.

METHODS

Conditioned extracellular matrixes were obtained by growing human umbilical vein endothelial cells in media containing 28 mmol/l hexoses (D-glucose, D-galactose, L-glucose), which undergo different intracellular processing, before and after adding the inhibitors of protein glycation thiamine or aminoguanidine. Having removed the endothelium, bovine retinal pericytes were grown on such matrixes and, in separate experiments, on laminin, fibronectin or type IV collagen. Pericyte adhesion was determined by cell counts 18 h after seeding.

RESULTS

Reduced adhesion was observed on matrixes produced in high D-glucose, high D-galactose and high L-glucose. Both thiamine and aminoguanidine restored impaired pericyte adhesion when added to high D-glucose and high D-galactose, but not L-glucose. Laminin, fibronectin and type IV collagen did not consistently modify pericyte adhesion.

CONCLUSIONS/INTERPRETATIONS

Pericyte adhesion is impaired on extracellular matrix produced by endothelium in high hexose concentrations. This could result from excess protein glycation, corrected by aminoguanidine and thiamine, rather than altered glycoprotein composition.

Risk factors for progression to proliferative diabetic retinopathy in the EURODIAB Prospective Complications Study

AIMS/HYPOTHESIS

Proliferative diabetic retinopathy (PDR), a leading cause of blindness, cannot be totally prevented by optimizing metabolic and blood pressure control and responds to no specific treatment other than partially destructive retinal photocoagulation. Recognizing risk factors using large-scale epidemiological studies could help identify targets for treatment. The EURODIAB Prospective Complications Study (PCS) includes the largest cohort so far of patients with Type I (insulin-dependent) diabetes mellitus.

METHODS

Baseline data were collected between 1989 and 1991 on 3250 patients who were recalled for follow-up. Physical examination, biochemical tests and assessment of complications were done on both occasions. In particular, 1249 patients had retinal photographs taken both basally and after an average of 7.3 years.

RESULTS

Proliferative retinopathy had developed in 157 patients (cumulative incidence 17.3/1000 patient-years; 95%-CI: 13.6-21.1). HbA(1c) (standardized regression estimate--SRE = 3.03, CI 2.49-3.69), diabetes duration (1.71, 1.42-2.06), age at diagnosis < 12 (1.66, 1.11-2.50), diastolic blood pressure less than or equal to 83 (1.50, 1.03-2.20) and waist-to-hip ratio (1.50, 1.03-2.20) were all independent predictors for progression to PDR when entered simultaneously into a logistic regression model. Including retinopathy at baseline maintained the effects of metabolic control and pre-pubertal onset only. Including the albumin excretion rate maintained the effect of control but reduced SRE for pre-pubertal onset to 1.49 (0.94-2.33). There was no evidence for a threshold effect for HbA(1c)concentrations at baseline and progression to proliferative retinopathy.

CONCLUSION/HYPOTHESIS

Metabolic control and duration of diabetes are strong indicators of progression to proliferative retinopathy. Onset of diabetes before puberty could be an additional independent risk factor.

A randomized controlled trial comparing three invitation strategies in a breast cancer screening program

BACKGROUND

The objective of this study was to compare the response received by a population-based breast cancer screening program, according to three different invitation strategies: letters sent by mail from the program (program group), letters sent by mail from the Primary Health Care Team (PHT group), and direct contact through a trained professional (direct contact group).

METHODS

We used a cluster-randomized controlled trial with assignment to invitation group using home address. Nine hundred eighty-six women of Barcelona (Spain), ages 50 to 64 years, were invited to participate in the program. The main outcome used was the response rate after the first invitation.

RESULTS

Five hundred sixty-four women accepted the invitation (57.2%). The highest response rate was achieved in the direct contact group (63.5%), followed by the PHT group (55.6%), the program group being the one that attained the lowest response rate (52.1%). The direct contact group had a higher probability of participating than the PHT group (RR = 1.14, P = 0.037) or the program group (RR = 1.22, P = 0.003). The response rate in the direct contact group was 72.1% when the letter was received by the subject herself. The increase in response occurred particularly among women of lower educational level.

CONCLUSIONS

Inviting women to participate in a breast cancer screening program through direct contact by trained personnel increased participation rate compared with mailed-letter methods. The positive effect appeared restricted to women with lower educational levels.

A comparative trial of botulinum toxin type A and methylprednisolone for the treatment of tension-type headache

Tension-type headache (TH) is a common condition, the pathophysiology of which remains undetermined. Evidence implicates sustained contraction of pericranial muscles to be a major cause. A recent preliminary study demonstrated the effectiveness of botulinum toxin type A (BTX-A) in patients suffering from chronic TH. To further investigate this, we performed a study to compare the efficacy of BTX-A with the steroid methylprednisolone (both administered with the local anesthetic lidocaine), when administered by injection into the tender points of cranial muscles in patients with TH. A significant decrease in the median pain score (assessed using a standard visual analogue scale ) was observed at 60 days post injection of BTX-A compared with the pain score achieved following steroid therapy. All patients treated with BTX-A experienced a gradual decrease in median pain severity scores at 30 days and 60 days post treatment. The beneficial effects of BTX-A therapy continued to improve 60 days following injection, whereas the effects of steroid therapy at this time point began to decline. This study clearly demonstrates the effectiveness of BTX-A for the treatment of TH.

Group visits improve metabolic control in type 2 diabetes: a 2-year follow-up

OBJECTIVE

To evaluate whether group visits, delivered as routine diabetes care and structured according to a systemic education approach, are more effective than individual consultations in improving metabolic control in non-insulin-treated type 2 diabetes.

RESEARCH DESIGN AND METHODS

In a randomized controlled clinical trial of 112 patients, 56 patients were allocated to groups of 9 or 10 individuals who participated in group consultations, and 56 patients (considered control subjects) underwent individual visits plus support education. All visits were scheduled every 3 months.

RESULTS

After 2 years, HbA(1c) levels were lower in patients seen in groups than in control subjects (P < 0.002). Levels of HDL cholesterol had increased in patients seen in groups but had not increased in control subjects (P = 0.045). BMI (P = 0.06) and fasting triglyceride level (P = 0.053) were lower. Patients participating in group visits had improved knowledge of diabetes (P < 0.001) and quality of life (P < 0.001) and experienced more appropriate health behaviors (P < 0.001). Physicians spent less time seeing 9-10 patients as a group rather than individually, but patients had longer interaction with health care providers.

CONCLUSIONS

Group consultations may improve metabolic control in the medium term by inducing more appropriate health behaviors. They are feasible in everyday clinical practice without increasing working hours.

Treatment of sialorrhoea with ultrasound guided botulinum toxin type A injection in patients with neurological disorders

OBJECTIVES

To investigate the safety and efficacy of ultrasound guided botulinum toxin type A (BTX-A) injections into salivary glands for the treatment of sialorrhoea in patients with neurological disorders.

METHODS

The parotid and submandibular glands of 10 patients were injected with BTX-A using ultrasound guidance. Before injection, the baseline rate of salivation was assessed using a visual analogue scale. Postinjection, assessments were repeated at regular intervals for up to 1 year.

RESULTS

Of the 10 patients treated, nine (90%) reported a subjective reduction in salivation post-treatment and one patient (10%) found no improvement. Visual analogue scale scores showed a reduction of 55% in the mean rate of salivation for all patients and a reduction of 60.8% for the group of responders. No serious adverse events occurred and no procedure related complications were reported.

CONCLUSIONS

This is the first study to report (1) the injection of BTX-A (BOTOX) into both parotid and submandibular glands, and (2) the use of ultrasound guidance during the administration of BTX-A into salivary glands. The results suggest that the technique is safe and that BTX-A injections are effective for the treatment of sialorrhoea in patients with neurological disorders.

Role of organochlorine compounds in the etiology of pancreatic cancer: a proposal to develop methodological standards

Studies on the possible role of organochlorine compounds in the etiology of pancreatic and other cancers face a set of methodologic and logistic issues that stem from the lipophilic nature of most organochlorines, and from the fact that tumor-induced lipid mobilization, weight loss, and metabolic changes can be profound before diagnosis. The question thus arises: do the xenobiotic concentrations in blood and adipose tissue result, in part, from such pathophysiologic changes? To assess and control potential selection and information biases, a flexible framework is warranted. It could be based on indicators such as time elapsed between the first symptom of cancer and blood or fat sample extraction; signs, symptoms and clinical status at the time of extraction; cholesterol and triglycerides levels; other laboratory findings; tumor stage at diagnosis; diagnostic procedures; treatment type and timing; clinical complications; and survival. Before adopting qualitative criteria and quantitative standards, their impact upon causal estimators should be assessed empirically.