Smoking as a confounder in case-control studies of occupational bladder cancer in women

Modifiable risk factors for the prevention of bladder cancer: a systematic review of meta-analyses

Each year, 430,000 people are diagnosed with bladder cancer. Due to the high recurrence rate of the disease, primary prevention is paramount. Therefore, we reviewed all meta-analyses on modifiable risk factors of primary bladder cancer. PubMed, Embase and Cochrane database were systematically searched for meta-analyses on modifiable risk factors published between 1995 and 2015. When appropriate, meta-analyses (MA) were combined in meta-meta-analysis (MMA). If not, the most comprehensive MA was selected based on the number of primary studies included. Probability of causation was calculated for individual factors and a subset of lifestyle factors combined. Of 1496 articles identified, 5 were combined in MMA and 21 were most comprehensive on a single risk factor. Statistically significant associations were found for current (RR 3.14) or former (RR 1.83) cigarette smoking, pipe (RR 1.9) or cigar (RR 2.3) smoking, antioxidant supplementation (RR 1.52), obesity (RR 1.10), higher physical activity levels (RR 0.86), higher body levels of selenium (RR 0.61) and vitamin D (RR 0.75), and higher intakes of: processed meat (RR 1.22), vitamin A (RR 0.82), vitamin E (RR 0.82), folate (RR 0.84), fruit (RR 0.77), vegetables (RR 0.83), citrus fruit (RR 0.85), and cruciferous vegetables (RR 0.84). Finally, three occupations with the highest risk were tobacco workers (RR 1.72), dye workers (RR 1.58), and chimney sweeps (RR 1.53). The probability of causation for individual factors ranged from 4 to 68 %. The combined probability of causation was 81.8 %. Modification of lifestyle and occupational exposures can considerably reduce the bladder cancer burden. While smoking remains one of the key risk factors, also several diet-related and occupational factors are very relevant.

Achievements and future of nutritional cancer epidemiology

We consider some of the earlier work and some recent results on diet and cancer (since the 2007 WCRF/AICR report on Diet and Cancer), discuss challenges facing nutritional cancer epidemiology, and consider the field from the perspective of the need to apply what we know in cancer control. We highlight 2 current difficulties; first, we are uncertain on the stage of carcinogenesis on which many nutritional factors act, second, we often do not know what dose of a nutritional factor is needed to achieve its expected protective effect in humans. Part of the difficulty is the measurement error associated with food frequency questionnaires. Calibration studies (as in the European Prospective Investigation on diet and Cancer) have helped to reduce this, and pooled studies have helped to clarify associations. However, there is too little work on new biomarkers of nutrition; with the new techniques available (especially proteomics, and metabolomics) it should be possible to identify more and better biomarkers that could be used in repeated blood or urine samples and give very good information on diet. In cancer control we need to determine how to reduce the prevalence of obesity and increase physical activity in populations, not whether they are causal factors. This could be achieved by community-based interventions linked to some of the new cohort studies being initiated. We conclude we have reached the stage in nutritional cancer epidemiology where we need to concentrate more on applying the lessons we have learnt, than in seeking new aetiological associations.

Shared occupational risks for transitional cell cancer of the bladder and renal pelvis among men and women in Sweden

BACKGROUND

Unlike cancer of the bladder, cancer of the renal pelvis is not considered an occupational cancer and little is known about risks among women.

METHODS

Using the Swedish national census and cancer registry-linked data (1971-1989), we identified transitional cell cancers of the renal pelvis (N = 1,374) and bladder (N = 21,591). Correlation between cancer sites for the standardized incidence ratios (SIR) were determined using Pearson's coefficient of the log SIR. Relative risks of job exposure matrix variables were calculated using Poisson regression.

RESULTS

Both cancer sites were significantly elevated among women and men employed in the machine/electronics industry, sedentary work, and indoor work, and men in the metal industry. The highest proportion of the bladder (12%) and renal pelvis (14%) cancers occurred among men employed in shop and construction metal work. Risks by industry were more correlated among women (r = 0.49, P = 0.002) than men (r = 0.24, P = 0.04). Cancers of the renal pelvis were elevated in several occupational and industry groups for which there was no elevated bladder cancer risk.

CONCLUSION

Cancers of the renal pelvis and bladder share common occupational risk factors that may be more frequent among women. In addition, there may be some jobs that pose an increased risk specifically for cancer of the renal pelvis but not bladder.

Bladder cancer risk in sales workers: artefact or cause for concern?

BACKGROUND

A large number of epidemiological studies have reported positive associations between bladder cancer and sales occupations. We investigated whether these findings are likely to be due to chance, confounding or publication bias, or may involve causal associations.

METHODS

Studies reporting bladder cancer risk-estimates for sales occupations were reviewed. Using meta-analyses we assessed heterogeneity and publication bias, and derived summary estimates.

RESULTS

Eighteen publications were identified, reporting 85 risk-estimates for sales-work. Meta-estimates were elevated for men (odds ratio (OR) 1.11, 95% confidence interval (CI) 1.01-1.21) and women (OR = 1.36, 95% CI = 1.11-1.67). The estimate was heterogeneous for men (p(Q-test) <0.01, women: 0.18) and indicated publication bias for women (p(Egger-test) <0.01, men: 0.40). When including only smoking-adjusted estimates reported irrespective of the strength of the association, the summary estimate for generic groups of sales workers was 0.99 (95% CI 0.90-1.08) for men, and 1.18 (95% CI = 0.99-1.39) for women, without statistically significant heterogeneity or publication bias. For women, risk was positively associated with longer duration of sales-employment in three studies.

CONCLUSIONS

Publication bias explained most of the reported increased bladder cancer risk, but sales-work still appeared to be associated with a small risk in women. Possible causal factors include lower frequency of urination and reduced fluid intake.

Total and specific fluid consumption as determinants of bladder cancer risk

We pooled the data from 6 case-control studies of bladder cancer with detailed information on fluid intake and water pollutants, particularly trihalomethanes (THM), and evaluated the bladder cancer risk associated with total and specific fluid consumption. The analysis included 2,729 cases and 5,150 controls. Odds ratios (OR) and 95% confidence intervals (CI) for fluid consumption were adjusted for age, gender, study, smoking status, occupation and education. Total fluid intake was associated with an increased risk of bladder cancer in men. The adjusted OR for 1 l/day increase in intake was 1.08, (95% CI 1.03-1.14, p-value for linear trend <0.001), while no trend was observed in women (OR=1.04, 0.94-1.15; p-value=0.7). OR was 1.33 (1.12-1.58) for men in the highest category of intake (>3.5 l/day) as compared to those in the lowest (<or=2 l/day). An increased risk was associated with intake of tap water. OR for >2 l/day vs. <or=0.5 l/day was 1.46 (1.20-1.78), with a higher risk among men (OR=1.50, 1.21-1.88). No increased risk was observed for the same intake groups of nontap water in men (OR=0.97, 0.77-1.22) or in women (OR=0.85, 0.50-1.42). Increased bladder cancer risks were observed for an intake of >5 cups of coffee daily vs. <5 and for THM exposure, but neither exposure confounded or modified the OR for tap water intake. The association of bladder cancer with tap water consumption, but not with nontap water fluids, suggests that carcinogenic chemicals in tap water may explain the increased risk.

Effect of different approaches to treatment of smoking as a potential confounder in a case-control study on occupational exposures

AIM

To evaluate the effect of different approaches to treatment of smoking as a potential confounder in an occupational study of lung cancer.

METHODS

Data were used from a case-control study on 956 men with lung cancer and 1253 population controls recruited in two northern Italian areas during 1990-1992. The risk of lung cancer associated with 11 selected job titles and eight selected industrial activities was estimated using seven different methods to treat smoking history. To evaluate the confounding effect of smoking, odds ratios obtained using the first six models were compared with estimates from the seventh and most complex model, in which cumulative tobacco consumption and time since cessation were considered.

RESULTS

Although crude odds ratios for some of the occupational categories were biased by up to 25%, such bias decreased to less than 10% when a simple model including smoking status (never, ex-, current) was used.

CONCLUSIONS

In occupational studies on lung cancer risk, information on smoking status may allow satisfactory control of the potential confounding effect of the habit.

Disinfection byproducts and bladder cancer: a pooled analysis

BACKGROUND

Exposure to disinfection byproducts in drinking water has been associated with an increased risk of bladder cancer. We pooled the primary data from 6 case-control studies of bladder cancer that used trihalomethanes as a marker of disinfection byproducts.

METHODS

Two studies were included from the United States and one each from Canada, France, Italy, and Finland. Inclusion criteria were availability of detailed data on trihalomethane exposure and individual water consumption. The analysis included 2806 cases and 5254 controls, all of whom had measures of known exposure for at least 70% of the exposure window of 40 years before the interview. Cumulative exposure to trihalomethanes was estimated by combining individual year-by-year average trihalomethane level and daily tap water consumption.

RESULTS

There was an adjusted odds ratio (OR) of 1.24 in men exposed to an average of more than 1 microg/L (ppb) trihalomethanes compared with those who had lower or no exposure (95% confidence interval [CI] = 1.09-1.41). Estimated relative risks increased with increasing exposure, with an OR of 1.44 (1.20-1.73) for exposure higher than 50 microg/L (ppb). Similar results were found with other indices of trihalomethane exposure. Among women, trihalomethane exposure was not associated with bladder cancer risk (0.95; 0.76-1.20).

CONCLUSIONS

These findings strengthen the hypothesis that the risk of bladder cancer is increased with long-term exposure to disinfection byproducts at levels currently observed in many industrialized countries.