Despite the rather grim picture that cancer of the lung commonly presents from the standpoint of operability and curability, it is of considerable importance to the physician for the following reasons:

1. It is now the leading cause of cancer death among men in the United States.

2. The incidence is increasing by approximately 2,000 cases annually, and there is every expectation that this trend will continue.

3. Because of the public debate which has developed over the relationship between smoking and lung cancer, many smokers are insisting on check-ups.

4. In view of this intense patient interest, it is important that the physician have the facts at his disposal so that he may answer questions and counsel his patients wisely.

5. It has been estimated that, in the absence of tobacco, up to 808 of lung cancer would not occur. It is thus largely a preventable disease.

Epidemiology. Incidence

Men

Women

38,000 new cases each year

5,700 new cases each year

14.78 of male cancer incidence

2.28 of female cancer incidence

Mortality

Men

Women

32,400 deaths each year

5,100 deaths each year

22.28 of male cancer mortality

4.18 of female cancer mortality

Rates And Ratios

Male

Female

Sex ratio

Incidence per 100,000

42.1

6.2

6.8 to 1

Mortality per 100,000

35.3

6.0

5.9 to 1

Age

Male

Female

Significant increase beyond age

40

50

Over 758 occurs between ages

50-75

50-75

Trend last ten years

Male

Female

Incidence-increase of

120.68

33.28

Mortality*-increase of

102.78

25.88

Geographic Distribution

The geographic distribution of cancer of the lung is given in Table 4.

Table 4. Geographic Distribution Of Cancer Of The Lung (Annual Mortality Per 100,000,1956-1957 )

Country

Male

Female

Sex ratio

Scotland

56.3

7.7

7.3:1

England and Wales

54.8

6.9

7.9:1

Finland

47.4

3.8

12.4:1

Austria

45.2

6 1

7.4:1

Netherlands

33.8

3.1

10.8:1

Germany, Federal Republic

29.5

4.1

7.1:1

New Zealand

27.4

3.4

8.0:1

Switzerland

27.2

3.2

8.5:1

United States (white population)

27.2

4.2

6.5:1

United States (nonwhite population)

25.2

4.3

5.9:1

Denmark

23.3

4.4

6.9:1

Australia

22.5

3.3

5.3:1

Canada

21.6

3.5

6.2:1

Ireland

21.3

5.8

3.7:1

France

18.1

3.4

5.4:1

Israel

17.7

7.8

2.3:1

Italy

17.0

3.4

4.9:1

Sweden

11.2

3 8

2.9:1

Norway

8.9

2.4

3.7:1

Japan

7.1

2.6

2.7:1

•Age-adjusted on combined population of forty-six countries in 1950. *From Segi, M.: Cancer Mortality for Selected Sites in Twenty-Four Countries (1950-1957), Sendai, Japan, 1960, Tohoku University School of Medicine.

The highest recorded death rates for lung cancer are in men in Scotland and in England and Wales, where the rates are approximately twice those for the

*Twenty-year trend shows a 218.2% increase for men and 45.5% increase for women.

United States calculated against a standardized population. Significantly lower rates are recorded in Sweden, Norway, and Japan. The possible etiologic factors are discussed below.

Etiology

Several factors have been suspected of being important in the causation of lung cancer.

Smoking

This is the single most important factor. It determines the distinctive age and sex pattern of most lung cancer as well as its alarming increase in frequency.

Although there remain a few vocal dissenters, the nearly unanimous conclusion has been reached as a result of innumerable epidemiologic studies that cigarette smoking is an important etiologic agent in epidermoid carcinoma of the lung. Some idea of the magnitude of this relationship can be gained from the following:

1. Epidermoid lung cancer is a very rare disease in nonsmokers.

2. It is almost 70 times as common among "two pack-a-day" smokers as among nonsmokers.

3. About one in eight long-term heavy smokers dies of the disease.

4. It has been estimated that approximately 808 of lung cancer as it is seen today would not occur were it not for smoking, particularly of cigarettes.

Occupation

Exposure to inhalants in industries using such substances as chromate, asbestos, beryllium, radioactive materials, petroleum products, etc. may be important in selected instances. The exposure must be prolonged and fairly intense. As a rule, it affects only a very small segment of the general population.

Residence

It has long been noted that lung cancer is more common among city dwellers than among those who live in the country. If the known difference in urban and rural smoking habits is taken into account, most of the disparity disappears. Nevertheless, a small increase in risk for the urban population persists; i.e., the nonsmoker in the city is slightly more prone to the disease than the nonsmoker in rural areas. This is presumably related to the factor of air pollution and, more specifically, to the type of air-bome contaminants encountered in a given area. Air pollution in one area may apparently increase the risk of lung cancer, whereas pollution of similar intensity in another area may play no role at all. Much work remains to be done in the identification of specific carcinogens in the atmosphere. It can be stated, however, that air pollution at its worst never begins to approach the etiologic significance of even average cigarette consumption.

Residence is a difficult factor to define and relate to individuals or groups and thus does not lend itself to study with the degree of precision possible for tobacco and other agents.