Question

1. A cohort study of smoking and bladder cancer was conducted in a small island population. There were a total of 1,000 people on the island. Four hundred were smokers and 600 were not. Fifty of the smokers developed bladder cancer. Ten of the non-smokers developed bladder cancer.
   1. What is the exposure and what is the disease?
   2. Set up the two by two table for these data with labels for exposures and disease status.
   3. Which measure of association/comparison should we use to assess the strength of the relationship between the exposure and disease?
   4. Calculate the correct measure and show your work.
   5. How do we interpret this effect estimate?

Answer 1

(a)Active cigarette smoking is a major risk factor for bladder cancer. exposure to cigarette smoke may also contribute to bladder carcinogenesis.

Smoking tobacco is the most important known risk factor for bladder cancer. Previous studies found that 20% to 30% of bladder cancer cases in women were caused by smoking. However, most of the earlier studies were conducted at times or in areas where smoking was much less common among women.

Smoking cigarettes, cigars or pipes may increase the risk of bladder cancer by causing harmful chemicals to accumulate in the urine. When you smoke, your body processes the chemicals in the smoke and excretes some of them in your urine.

The exposure is smoking and disease is bladder cancer.

Exposure

(a) exposure**

Exposure	smoking status
400 people	active smokers
600 people	secondhand smokers

Disease status**

Disease status	smoking status
Bladder cancer	50 out of 400
Second exposure of smoking	10 out of 600

(c) The basis of an extensive body of scientific evidence, active cigarette smoking has been considered to be causally associated with bladder cancer. The evidence from cohort studies has been remarkably consistent in indicating a twofold or greater excess risk of developing or dying from bladder cancer among current smokers compared with never A meta-analysis of observational epidemiologic studies estimated that, compared with never smokers, the risk of urinary tract (primarily bladder) cancer was elevated more than threefold among current smokers and twofold among former smokers . Active cigarette smoking is a major contributor to the population burden of bladder cancer. To augment the already extensive evidence from case-control studies, additional evidence from large cohort studies is valuable for more precisely characterizing the risks of active cigarette smoking and strengthening the overall foundation for making the claim of a causal association.

The causal relation between active cigarette smoking and bladder cancer provides reason to suspect that secondhand cigarette smoke (also known as environmental tobacco smoke or passive smoke) may also contribute to bladder carcinogenesis. As with active cigarette smoking, secondhand cigarette smoke contains arylamines, which are established bladder carcinogens . The dose of carcinogen exposure from secondhand smoke is less than that from active cigarette smoking, but even so, the relatively low dose of carcinogens from secondhand smoke exposure has been hypothesized to make a disproportionately large contribution to bladder carcinogenesis .This is because, among persons exposed to cigarette smoke, those who are genetically more susceptible to tobacco toxins are hypothesized to have greater bladder cancer risks in general but also risks that are disproportionately higher at low levels of exposure . The plausibility of an association between secondhand smoke and bladder cancer is further strengthened by the fact that carcinogens have been measured in the urine of passive smokers showing that carcinogens from secondhand smoke come into direct contact with the bladder.

The hypothesis that secondhand smoke exposure is a risk factor for bladder cancer has only rarely been explored in epidemiologic studies, despite the established link between active cigarette smoking and bladder cancer and a strong rationale for suspecting that secondhand cigarette smoke exposure could contribute to bladder carcinogenesis.

(d)Collection of smoking information on all household members directly provided the data with which to investigate active cigarette smoking habits and, by determining whether a never smoker resided with a cigarette smoker, a measure of household exposure to secondhand smoke. Respondents classified their active cigarette smoking status into one of three categories: never, former, or current smoking.

(e) prospective cohort study provide further confirmation of the important role that active cigarette smoking plays in the etiology of bladder cancer. The marked elevation in risk associated with active smoking provides additional data which further support the evidence that smoking causes bladder cancer.