# Relationship of smoking and lung cancer

### CDC - What Are the Risk Factors for Lung Cancer?

studies that have examined the relationship between smoking and lung cancer. The mean age at onset of regular cigarette smoking has been less than 20 years . Observational cohort studies were included if they reported sex-specific RRs or equivalent, on the relationship between smoking and lung cancer. Studies were. The most important risk factor for lung cancer is tobacco smoking, and the data supporting this relationship are compelling (1). Compared with nonsmokers.

For example, the smoking prevalence for age 20—29 among those born in — is assumed to be the same as that of For a certain 5-year age group, the lung cancer death rate varies by gender and also by birth cohort.

## Link between smoking and cancer

This difference gives an opportunity to estimate quantitatively the increment of lung cancer death rate for that 5-year age group in relation to the unit increase in cumulative cigarette consumption. This analysis is done for both genders combined as follows: In summing the cumulative cigarette consumption for a certain birth cohort, the reduction in lung cancer risk in ex-smokers is taken into account by Equation 1.

The parameters Ai and Bi are estimated for each age group i. Validation of estimated functions by comparison with published data As the next step, the validity of the quantitative relationship based on Equation 2 is examined by comparing lung cancer deaths expected from the equation with observed deaths in past studies.

The prerequisite for such studies is that the cumulative cigarette consumption of the study subjects can be estimated from reported data. The lung cancer incidence or mortality in the study subjects should also be available.

Since there is no epidemiological study satisfying this prerequisite in Japan, the following two studies were selected. For women, the expected number of lung cancer deaths is calculated for all smokers combined because the total observed person-years were not sufficient to enable subset analysis. The number of cigarettes consumed daily was reported for five categories: To calculate the cumulative cigarette consumption, 0, 5, 15, 30, and 50 cigarettes are assigned for these categories, respectively.

The person-years of observation were provided for 5-year age groups from 55 to 74, which can be used to calculate the expected number of lung cancer deaths by applying the lung cancer death rates expected from Equation 2. The second data set is from the prospective cohort study of British male physicians. The smokers started smoking between 15 and 24 years of age average age The strength of this data set is that the smokers were restricted to those whose daily cigarette consumption varied by less than 5 cigarettes during the follow-up.

This enables precise estimation of the cumulative cigarette consumption of the cohort. The average number of cigarettes consumed per day were reported as 0, 2. The results of the present study are used to estimate the expected number of lung cancer deaths, while the observed number are incident cases of lung cancer. Taking into account the low survival rate among lung cancer patients, it was decided that the observed number of lung cancer cases can be compared with the expected number of lung cancer deaths.

Results Estimation of cumulative cigarette consumption The cumulative cigarette consumption was estimated for those born — Figure 1. Except for a temporary decrease corresponding to the deficit of sales shortly after World War II, the cumulative cigarette consumption was found to have increased in later birth cohorts for all ages of males and females.

As can be seen, the increases seem to have occurred uniformly across different age groups. The increment of cumulative consumption by one-year shift in year of birth ranged from to for males and from 80 to for females.

The ratio of cumulative cigarette consumption among males to females was approximately 5: Analysis of lung cancer death rate in relation to cumulative cigarettes consumption For the 5-year age groups 35—39 to 70—74, the lung cancer death rates of different birth cohorts of males and females were plotted against the cumulative cigarette consumption Figure 2.

Note that the vertical axes were adjusted in different age groups, so that the increasing trends could be observed. A statistically significant positive correlation was observed for the lung cancer death rates of those aged 35—39 to 70—74 in relation to corresponding cumulative cigarette consumption.

When the correlation was examined in Figure 2the difference in lung cancer death rate between males and females seems to be explained solely by the difference in cumulative cigarette consumption. Validation of estimated functions by comparison with published data In the cohort study of the American Cancer Society, the observed lung cancer deaths for male and female smokers were 33 andwhereas the numbers of deaths expected from Equation 2 were The observed numbers for male and female never-smokers were 77 and 27, whereas the numbers expected from Equation 2 were The agreement for never-smokers was not so good as for current smokers.

In the cohort study of British physicians, the observed incident cases of lung cancer were reported by nine different smoking categories Table 1.

The expected numbers of lung cancer deaths estimated from the observed person-years and cumulative cigarette consumption are also shown in Table 1.

The observed total number of lung cancer incident cases showed good agreement with the number of cases expected from the present study; versus When the observed numbers in different smoking categories were compared with expected values, the agreement varied by smoking categories. According to the quantitative analysis of the cohort data by Doll and Peto, 5 the lung cancer incidence rate was shown to increase in proportion to the smoking duration raised to the power of 4. In comparison, the slope of linear equations shown in Figure 2 was found to increase in proportion to the 4.

Thus, it was suggested that the increasing slope of linear equations by age reflected implicitly the effect of increasing smoking duration.

### How does smoking cause cancer? | Cancer Research UK

Discussion The present study introduced the idea of cumulative cigarette consumption and showed successfully that the lung cancer death rate of Japanese males and females in the age groups 35—39 to 70—74 increased in proportion to the cumulative cigarette consumption at a national level.

The aim of this study is not to prove the causal relationship between cigarette smoking and lung cancer death, but to provide quantitative formulae by which lung cancer mortality at a national level can be analysed and predicted from the cigarette smoking of the Japanese population. In this regard, the results of the present study seem to be promising, because the fit of the linear equations to the observed data is highly significant Figure 2.

The results of the present study were further validated by applying the equations to two cohort studies in the US and UK. The comparisons of observed and expected lung cancer deaths in the American cohort study and incident cases in the British cohort study both showed good agreement. Furthermore, the slope of linear equations increases in proportion to the 4.

This is in good agreement with the British cohort study, in which the lung cancer incidence rate increased in proportion to the 4. The increase in cumulative cigarette consumption, as shown in Figure 1can explain the increase in lung cancer mortality of males and females by simply applying the linear equations shown in Figure 2.

There are arguments that the increase in lung cancer incidence and mortality among women could be due to factors other than cigarette smoking, and efforts are being made to identify such factors.

The present study showed successfully that no other factors than smoking are necessary to explain the increase in lung cancer mortality of both males and females in Japan. The quantitative formulae are also useful for predicting the future of lung cancer mortality in Japan. An increasing trend was seen in the cumulative cigarette consumption in most ages of males and females Figure 1.

If this trend continues in the future, the lung cancer death rate in Japan can be predicted to continue increasing according to the regression lines shown in Figure 2. The impact of tobacco control at the national level on lung cancer mortality in the future can also be assessed using these formulae.

Several issues relate to the validity of the present study. Even smoking a few cigarettes a day or smoking occasionally increases the risk of lung cancer.

The more years a person smokes and the more cigarettes smoked each day, the more risk goes up. People who quit smoking have a lower risk of lung cancer than if they had continued to smoke, but their risk is higher than the risk for people who never smoked. Quitting smoking at any age can lower the risk of lung cancer.

## How does smoking cause cancer?

Cigarette smoking can cause cancer almost anywhere in the body. Cigarette smoking causes cancer of the mouth and throat, esophagus, stomach, colon, rectum, liver, pancreas, voicebox larynxtrachea, bronchus, kidney and renal pelvis, urinary bladder, and cervix, and causes acute myeloid leukemia. Secondhand Smoke Secondhand smoke and the harmful chemicals in it are known causes of sudden infant death syndrome, respiratory infections, ear infections, and asthma attacks in infants and children.

They are also known causes of heart disease, stroke, and lung cancer in adult nonsmokers. When a person breathes in secondhand smoke, it is like he or she is smoking.

Radon Radon is a naturally occurring gas that comes from rocks and dirt and can get trapped in houses and buildings. It cannot be seen, tasted, or smelled. According to the U.

Environmental Protection Agency EPAradon causes about 20, cases of lung cancer each year, making it the second leading cause of lung cancer. Nearly one out of every 15 homes in the United States is thought to have high radon levels. The EPA recommends testing homes for radon and using proven ways to lower high radon levels.