Patients with epidermoid cancer anywhere in the respiratory or upper alimentary tract should be identified as being at high-risk for the development of new lesions in the same general area but not necessarily related or in proximity to the first lesion. Under these circumstances, the incidence of multiple primary lesions in the oral cavity, larynx, lung, and related structures is inordinately high. Unquestionably, it would be much higher were not the first cancer fatal to the patient so often and in such a short period of time.

Pathology

The vast majority of malignant pulmonary neoplasms arise from the bronchial epithelium, and thus the term lung cancer is almost synonymous with bronchogenic carcinoma.

Classification

Considerable variation in terminology exists regarding the nomenclature and classification of carcinoma of the lung according to the microscopic picture presented to the pathologist or cytologist. Lung cancers which are indistinguishable clinically may show a wide variation in their histologic pictures.

For clinical purposes, the following classification of bronchial carcinoma is satisfactory:

Squamous Cell Carcinoma

This is the most common type, occurring predominantly in males (ratio 10:1) in their mid-50's and 60's and related to extrinsic factors such as cigarette smoking. It arises from metaplastic squamous epithelium.

Oat Cell (Small Cell) Carcinoma

This is less common but has an age, sex, and epidemiologic pattern similar to that of squamous cell carcinoma. It arises from reserve cells in the basal layer of the bronchial mucosa. Because of its tendency to extend below the basal layer rather than grow into the bronchial lumen, oat cell carcinoma characteristically is diagnosed late in its course and carries the poorest prognosis of the various histologic types.

Adenocarcinoma (Mucus-Secreting)

This form of lung cancer occurs with equal frequency in males and females. It is the most common form in women and the third most frequent in men. The patients are slightly younger than those with epidermoid lesions, with a peak between 40 and 55 years of age. There is no established relationship to extrinsic factors. This type arises from the glandular epithelium of the bronchi.

Terminal Bronchiolar Carcinoma (Alveolar Cell Carcinoma)

As the two names imply, confusion exists regarding the origin of this form of lung cancer. It is seen with equal frequency in men and women and may occur at any age.

Anaplastic And Undifferentiated Bronchial Carcinoma

These may relate to any of the preceding categories. The proportion of bronchial carcinomas classified as anaplastic and undifferentiated varies from pathologist to pathologist and is apt to diminish with more intensive pathologic study.

Bronchial Carcinoid (Bronchial Adenoma)

This relatively rare entity is listed because of its occasional confusion clinically with the more classical bronchogenic carcinoma. Even more important, however, is the fact that approximately half of these histologically "benign" adenomas may metastasize and otherwise behave in a malignant fashion. These tumors mirror carcinoids of the gastrointestinal tract both in histologic appearance and in clinical behavior. Bronchial adenomas occur in younger age groups with approximately equal distribution between males and females.